Fix the inconsistent message sequence negotiation during connection/pipe reset.

During connection reset (mark_down at one side), if there is an existing connection at peer side which is not cleared yet, it could bring inconsistent sequence negotiation problem which crash OSD deamon, please refer to http://tracker.ceph.com/issues/8232#note-17 for detailed analysis in terms of how the race could happen.

Signed-off-by: Guang Yang (yguang@yahoo-inc.com)