io_uring/cmd_net: use READ_ONCE() for ->addr3 read

io_uring/cmd_net: use READ_ONCE() for ->addr3 read

Any SQE read should use READ_ONCE(), to ensure the result is read once
and only once. Doesn't really matter for this case, but it's better to
keep these 100% consistent and always use READ_ONCE() for the prep side
of SQE handling.

Fixes: 5d24321e4c15 ("io_uring: Introduce getsockname io_uring cmd")
Signed-off-by: Jens Axboe <axboe@kernel.dk>