fix ICMPv6 on freebsd2 (and perhaps bsdi3).  I made a mistake in enabling tcp4/udp4 on bsdi4 (I erased wrong #endif).
fix ICMPv6 on freebsd2 (and perhaps bsdi3).  I made a mistake in enabling
tcp4/udp4 on bsdi4 (I erased wrong #endif).

MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame