Write-back throttling (WBT) enables QUEUE_FLAG_STATS on the request
queue. But WBT does not make sense for passthrough io, so skip
QUEUE_FLAG_STATS processing.

Also skip rq_qos_issue/done for passthrough io.

Overall, the change gives ~11% hike in peak performance.
Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20231123190331.7934-1-kundan.kumar@samsung.comSigned-off-by: Jens Axboe <axboe@kernel.dk>