io_uring/net: reject SEND_VECTORIZED when unsupported

io_uring/net: reject SEND_VECTORIZED when unsupported

IORING_SEND_VECTORIZED with registered buffers is not implemented but
could be. Don't silently ignore the flag in this case but reject it with
an error. It only affects sendzc as normal sends don't support
registered buffers.

Fixes: 6f02527729bd3 ("io_uring/net: Allow to do vectorized send")
Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>