lockd: server should unlock lock if client rejects the grant

Currently lockd just dequeues the block and ignores it if the client
sends a GRANT_RES with a status of nlm_lck_denied. That status is an
indicator that the client has rejected the lock, so the right thing to
do is to unlock the lock we were trying to grant.

Reported-by: Yongcheng Yang <yoyang@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2063818


Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>