rbd-mirror: fix possible recursive lock of ImageReplayer::m_lock

rbd-mirror: fix possible recursive lock of ImageReplayer::m_lock

If periodic status update (LambdaContext which is queued from
handle_update_mirror_image_replay_status()) races with shutdown and
ends up being the last in-flight operation that shutdown was pending
on, we attempt to recursively acquire m_lock in shut_down() because
m_in_flight_op_tracker.finish_op() is called with m_lock (and also
m_threads->timer_lock) held.  These locks are needed only for the call
to schedule_update_mirror_image_replay_status() and should be unlocked
immediately.

Fixes: https://tracker.ceph.com/issues/69978
Co-authored-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: N Balachandran <nithya.balachandran@ibm.com>