ceph: fix flush_snap logic after putting caps

ceph: fix flush_snap logic after putting caps

A primary reason for skipping ceph_check_caps after putting the
references was to avoid the locking in ceph_check_caps during a
reconnect. __ceph_put_cap_refs can still call ceph_flush_snaps in that
case though, and that takes many of the same inconvenient locks.

Fix the logic in __ceph_put_cap_refs to skip flushing snaps when the
skip_checking_caps flag is set.

Fixes: e64f44a88465 (ceph: skip checking caps when session reconnecting and releasing reqs)
Signed-off-by: Jeff Layton <jlayton@kernel.org>