NFSD: add encoding of op_recall flag for write delegation

Modified nfsd4_encode_open to encode the op_recall flag properly
for OPEN result with write delegation granted.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: stable@vger.kernel.org