ceph: don't re-send interrupted flock request

Don't re-send interrupted flock request in cases of mds failover
and receiving request forward. Because corresponding 'lock intr'
request may have been finished, it won't get re-sent.

Link: http://tracker.ceph.com/issues/20170


Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>