ublk driver started to take plain command encoding, which turns out
one bad way. The traditional ioctl command opcode encodes more
info and basically defines each code uniquely, so opcode conflict
is avoided, and driver can handle wrong command easily, meantime it
may help security subsystem to audit io_uring command.

Say Y if your application still uses legacy command opcode.

Say N if you don't want to support legacy command opcode. It is
suggested to enable N if your application(ublk server) switches to
ioctl command encoding.