Fix the experimental NFS client so that it doesn't panic when

NFSv2,3 byte range locking is attempted. A fix that allows the
nlm_advlock() to work with both clients is in progress, but
may take a while. As such, I am doing this commit so that
the kernel doesn't panic in the meantime.

Submitted by:	jh
MFC after:	2 weeks

sys/fs/nfsclient/nfs_clvnops.c

@@ -2939,8 +2939,10 @@ nfs_advlock(struct vop_advlock_args *ap)
 		} else {
 			if (ncl_advlock_p)
 				error = ncl_advlock_p(ap);
-			else
+			else {
+				VOP_UNLOCK(vp, 0);
 				error = ENOLCK;
+			}
 		}
 	}
 	return (error);