Remove ctl(4) from GENERIC.  Also remove 'options CTL_DISABLE'
and kern.cam.ctl.disable tunable; those were introduced as a workaround
to make it possible to boot GENERIC on low memory machines.

With ctl(4) being built as a module and automatically loaded by ctladm(8),
this makes CTL work out of the box.

Reviewed by:	ken
Sponsored by:	FreeBSD Foundation
Reflect removing of the counter_u64_subtract() function in the macro.
Fix usage for soreceive(9) - uio must always be non-NULL.

MFC after:	1 week
Add some more dates and relationships.

Submitted by:	jkoshy, gj, dfr