crimson/monc: close() active_con before destructing it on resets.

crimson/monc: close() active_con before destructing it on resets.

`ProtocolV2` expects `AuthClient` implementations to withstand
calling `get_auth_request()` and `handle_auth_reply_more()` even
if `handle_auth_done()` had been already called. This is because
a network fault may happen on e.g. `AuthSignatureFrame` which is
put on the wire after the `AuthDone` handling.

`crimson::mon::Client` deals with that by returning `auth::error`
from both `get_auth_request()` and `handle_auth_reply_more()` as
the preceding invocation of `handle_auth_done()` had already
cleared `pending_conns` (and set `active_con`). This leads to
`abort_in_close()` and finally to dispatching `ms_handle_reset()`
on `mon::Client` which is fine in general but, when comes to the
current implementation, it destroys `active_con` without closing
it first.
One of the consequence is breaking the `mon::Connection::reply`
promise; another one is missed `mark_down()` call.

```
DEBUG 2021-03-01 18:10:50,489 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@56752 >> mon.? v2:172.21.15.110:3300/0] GOT AuthDoneFrame: gid=4121, con_mode=se
cure, payload_len=995
DEBUG 2021-03-01 18:10:50,489 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@56752 >> mon.? v2:172.21.15.110:3300/0] WRITE AuthSignatureFrame: signature=60ca
f49e5a6cf3cc39c4160cb9d09032db5f794e29655dc0124cf5f42b7546fb
DEBUG 2021-03-01 18:10:50,489 [shard 0] ms - authenticated_encrypt_update plaintext.length()=80 buffer.length()=80
DEBUG 2021-03-01 18:10:50,489 [shard 0] ms - authenticated_encrypt_final buffer.length()=96 final_len=0
INFO  2021-03-01 18:10:50,489 [shard 0] monc - found mon.noname-a
INFO  2021-03-01 18:10:50,489 [shard 0] monc - sending auth(proto 2 2 bytes epoch 0) v1
INFO  2021-03-01 18:10:50,489 [shard 0] monc - waiting
DEBUG 2021-03-01 18:10:50,489 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@56752 >> mon.? v2:172.21.15.110:3300/0] GOT AuthSignatureFrame: signature=ea04f1
318cf76808414a853ed37fd232ae886bef036cb4248079c6cba89d669a
DEBUG 2021-03-01 18:10:50,490 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@56752 >> mon.? v2:172.21.15.110:3300/0] WRITE ClientIdentFrame: addrs=v2:172.21.
15.110:6800/33954, target=v2:172.21.15.110:3300/0, gid=0, gs=1, features_supported=4540138303579357183, features_required=576460752303432193, flags=1, cookie=9231904580
14536120
...
INFO  2021-03-01 18:10:50,490 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@56752 >> mon.? v2:172.21.15.110:3300/0] execute_connecting(): fault at CONNECTIN
G, going to WAIT -- std::system_error (error crimson::net:4, read eof)
...
DEBUG 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@0 >> mon.? v2:172.21.15.110:3300/0] GOT HelloFrame: my_type=mon peer_addr=v2:172.21.15.110:63960/0
INFO  2021-03-01 18:10:50,690 [shard 0] monc - get_auth_request(con=[osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0], auth_method=0)
ERROR 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] get_initial_auth_request returned crimson::auth::error (unknown connection)
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] closing: reset yes, replace no
DEBUG 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] TRIGGER CLOSING, was CONNECTING
...
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] write_event: dropped
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] execute_connecting(): protocol aborted at CLOSING -- std::system_error (error crimson::net:6, protocol aborted)
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] closing: reset yes, replace no
DEBUG 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] TRIGGER CLOSING, was CONNECTING
WARN  2021-03-01 18:10:50,690 [shard 0] osd - ms_handle_reset
WARN  2021-03-01 18:10:50,690 [shard 0] monc - active conn reset v2:172.21.15.110:3300/0
INFO  2021-03-01 18:10:50,690 [shard 0] monc - reopen_session to mon.-1
WARN  2021-03-01 18:10:50,690 [shard 0] monc - mon.0 does not have an addr compatible with me
INFO  2021-03-01 18:10:50,690 [shard 0] monc - connecting to mon.1
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954 >> mon.? v2:172.21.15.110:3300/0] ProtocolV2::start_connect(): peer_addr=v2:172.21.15.110:3300/0, peer_name=mon.?, cc=14512795460730278364 policy(lossy=true, server=false, standby=false, resetcheck=false)
DEBUG 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954 >> mon.? v2:172.21.15.110:3300/0] TRIGGER CONNECTING, was NONE
DEBUG 2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954 >> mon.? v2:172.21.15.110:3300/0] UPDATE: gs=3 for connect
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954 >> mon.? v2:172.21.15.110:3300/0] write_event: delay ...
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] write_event: dropped
INFO  2021-03-01 18:10:50,690 [shard 0] ms - [osd.0(client) v2:172.21.15.110:6800/33954@63960 >> mon.? v2:172.21.15.110:3300/0] execute_connecting(): protocol aborted at CLOSING -- std::system_error (error crimson::net:6, protocol aborted)
...
"
WARN  2021-03-01 18:10:50,690 [shard 0] seastar - Exceptional future ignored: seastar::broken_promise (broken promise), backtrace:    0x146f364
   0x146f6e1
   0x146fb01
   0x135c2fe
   0x135c481
   0x6ee079
   0x137db87
   0x137def2
   0x13ab085
   0x1347b27
   0x6619f5
   /lib64/libc.so.6+0x237b2
   0x6b217d
   --------
   N7seastar12continuationINS_8internal22promise_base_with_typeIvEENS_6futureIvE12finally_bodyIZNS_5asyncIZZ4mainENKUlvE_clEvEUlvE_JEEENS_8futurizeINSt9result_ofIFNSt5decayIT_E4typeEDpNSC_IT0_E4typeEEE4typeEE4typeENS_17thread_attributesEOSD_DpOSG_EUlvE1_Lb0EEEZNS5_17then_wrapped_nrvoIS5_SU_EENSA_ISD_E4typeEOT0_EUlOS3_RSU_ONS_12future_stateINS1_9monostateEEEE_vEE

```

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>