io_uring/net: use struct io_br_sel->val as the send finish value

Currently a pointer is passed in to the 'ret' in the send mshot handler,
but since we already have a value field in io_br_sel, just use that.
This is also in preparation for needing to pass in struct io_br_sel
to io_send_finish() anyway.

Link: https://lore.kernel.org/r/20250821020750.598432-11-axboe@kernel.dk


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