test/cq-overflow.c: add IO test
test/cq-overflow.c: add IO test

Try and provoke drops with actual IO, check if things are handled
correctly.

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing