selftests: ublk: kublk: use ioctl-encoded opcodes

There are a couple of places in the kublk selftests ublk server which
use the legacy ublk opcodes. These operations fail (with -EOPNOTSUPP) on
a kernel compiled without CONFIG_BLKDEV_UBLK_LEGACY_OPCODES set. We
could easily require it to be set as a prerequisite for these selftests,
but since new applications should not be using the legacy opcodes, use
the ioctl-encoded opcodes everywhere in kublk.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250401-ublk_selftests-v1-1-98129c9bc8bb@purestorage.com


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