When clearing out the scheduler queues during system shutdown, we move
all processes to the SSTOP state.  Make sure we update each process's
p_waited and the parents' p_nstopchild counters to maintain consistent
values.  Should not make any real difference this late in the shutdown
process, but we should still be consistent just in case.

Fixes PR kern/50318

Pullups will be requested for:

      NetBSD-7, -6, -6-0, -6-1, -5, -5-0, -5-1, and -5-2

(pgoyette)