MFC r265323 (by trasz):
Provide better descriptions for 'struct ctl_scsiio' fields; based mostly
on emails from ken@.
MFC r267481, r267952:
Implement small KPI to access LUN options instead doing it by hands.
MFC r267485:
Remove non-functional remnants of control LUN -- 18MB of RAM for nothing.
MFC r267496, r267498:
Add "vendor", "product" and "revision" options to control inquiry data.
MFC r267499:
Remove custom processing for "file" option.
MFC r267500:
Format Portal Group Tag same as istgt does -- %4.4x instead of %x.

SPC-4 spec tells it should be "two or more hexadecimal digits".
RFC3720 tells it is 16-bit value.
MFC r267514:
Move kern_total_len setting from backend to core code.