io_uring/zcrx: add selftest case for recvzc with read limit

Add a selftest case to iou-zcrx where the sender sends 4x4K = 16K and
the receiver does 4x4K recvzc requests. Validate that the requests
complete successfully and that the data is not corrupted.

Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://lore.kernel.org/r/20250224041319.2389785-3-dw@davidwei.uk


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