scsi: core: Move command size detection out of the fast path

We only need to detect the command size for ioctl request from userspace,
which is limited to the passthrough path.  Move the check there instead of
doing it for all queuecommand invocations.

Link: https://lore.kernel.org/r/20201005084130.143273-4-hch@lst.de


Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>