io_uring/net: don't lose partial send/recv on fail

Just as with rw, partial send/recv may end up in
io_req_complete_failed() and loose the result, make sure we return the
number of bytes processed.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a4ff95897b5419356fca9ea55db91ac15b2975f9.1663668091.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>