test/recvsend_bundle-inc: various fixes and cleanups

- Free allocated buffers for each run
- Get rid of next_bid checking, everything is bid == 0 anyway. So check
  for that specifically.
- Check that IORING_CQE_F_BUF_MORE is always set, as we never run out
  of buffers

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