Overhaul ppp(8) build options so they are safe to use in
/etc/make.conf:
NOALIAS -> retired (support provided by PPP_NO_NAT)
NOATM -> PPP_NO_ATM (also subject to NO_ATM global)
NODES -> PPP_NO_DES (support was broken, now recovered)
NOI4B -> PPP_NO_I4B (also subject to NO_I4B global)
NOKLDLOAD -> PPP_NO_KLDLOAD
NONAT -> PPP_NO_NAT
NONETGRAPH -> PPP_NO_NETGRAPH
NOPAM -> PPP_NO_PAM (will be subject to NO_PAM global)
NORADIUS -> PPP_NO_RADIUS
NOSUID -> retired (support provided by PPP_NO_SUID)
PPP_NOSUID -> PPP_NO_SUID
dd991de030