selftests/net: don't tests batched TCP io_uring zc

It doesn't make sense batch submitting io_uring requests to a single TCP
socket without linking or some other kind of ordering. Moreover, it
causes spurious -EINTR fails due to interaction with task_work. Disable
it for now and keep queue depth=1.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b547698d5938b1b1a898af1c260188d8546ded9a.1666700897.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>