Improve uniformity in the kernel of handling of request operation and
flags by passing these as a single argument.

Cc: Song Liu <song@kernel.org>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-32-bvanassche@acm.orgSigned-off-by: NJens Axboe <axboe@kernel.dk>