locks: allow support for write delegation

Remove the check for F_WRLCK in generic_add_lease to allow file_lock
to be used for write delegation.

First consumer is NFSD.
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/locks.c

@@ -1729,13 +1729,6 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr
 	if (is_deleg && !inode_trylock(inode))
 		return -EAGAIN;
 
-	if (is_deleg && arg == F_WRLCK) {
-		/* Write delegations are not currently supported: */
-		inode_unlock(inode);
-		WARN_ON_ONCE(1);
-		return -EINVAL;
-	}
-
 	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	time_out_leases(inode, &dispose);