AsyncConnection: Don't increment connect_seq if connect failed

AsyncConnection: Don't increment connect_seq if connect failed

If connection sent many messages without acked, then it was marked down.
Next we get a new connection, it will issue a connect_msg with connect_seq=0,
server side need to detect "connect_seq==0 && existing->connect_seq >0",
so it will reset out_q and detect remote reset. But if client side failed
before sending connect_msg, now it will issue a connect_msg with non-zero
connect_seq which will cause server-side can't detect exist remote reset.
Server-side will reply a non-zero in_seq and cause client crash.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>