minor makefile delint

MKfoo=no -> NOfoo

convert from NOxxx= to MKxxx=no.
include <bsd.own.mk> if testing a MKxxx variable.

move (using repository copy) bootp{d,ef,gw,test} into a common hierarchy
with a libcommon - to stop unnecessary recompilation of the source.
add Makefile* to suit.