io_uring/net: use right helpers for async_data

There is another spot where we check ->async_data directly instead of
using req_has_async_data(), which is the way to do it, fix it up.

Fixes: 43e0bbbd ("io_uring: add netmsg cache")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/42f33b9a81dd6ae65dda92f0372b0ff82d548517.1660822636.git.asml.silence@gmail.com


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