PATCH: Disable 6 byte commands for USB, firewire, ATAPICAM

Attached is a patch that disables ever sending 6 byte commands to buses
that do not support them.  Numerous USB devices hang when receiving a 6
byte command.  For testing, this patch comments out the scsi_da quirks for
devices that I believe are addressed by this patch and no longer need the
quirk.

Please test devices such as USB keys, USB cameras, Firewire hard disks,
and ATAPICAM cd drives to be sure they still work with this patch.
Especially if you've needed a quirk before, it is important to see if this
patch does not break your device.  I hope to get this into the tree early
so there is plenty of testing before 5.2.

Thanks,
Nate