Currently, if a process is exiting and its parent has indicated no intent
of reaping the process (nor any other children), the process wil get
reparented to init.  Since the state of the exiting process at this point
is SDEAD, proc_reparent() will not update either the old or new parent's
p_nstopchild counters.

This change causes both old and new parents to be properly updated.

Fixes PR kern/50300

Pullups will be requested for:

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

(pgoyette)