rbd: lock should be quiesced on reacquire

Quiesce exclusive lock at the top of rbd_reacquire_lock() instead
of only when ceph_cls_set_cookie() fails.  This avoids a deadlock on
rbd_dev->lock_rwsem.

If rbd_dev->lock_rwsem is needed for I/O completion, set_cookie can
hang ceph-msgr worker thread if set_cookie reply ends up behind an I/O
reply, because, like lock and unlock requests, set_cookie is sent and
waited upon with rbd_dev->lock_rwsem held for write.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>