The feature to block queues is quite dubious, since it races with in-flightAcked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
IO. Indeed, it seems unnecessary for block queues for any times we do so.
Anyway, to keep the same behaviour, use standard SCSI API to stop IO being
sent - scsi_{un}block_requests().
Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>