ip6.h is almost normal RFC2292 header.
icmp6.h has couple of extensions (not covered by RFC2292),
like MLD, ICMPv6 nodeinfo, and router renumber.
XXX how to synchronize with future kame changes?
Hope I did not break anything. Portability on IPv4-only node needs checking,
I'll do this very soon. (sorry for rather jumbo commit)
XXx what is _FAVOR_BSD?