* kame/sys/netinet6/natpt_{dispatch,tslot,var}.[ch]: - Support translation from ICMPv6 that occurred with IPv6 host   into ICMPv4 in "IPv4->IPv6" translation.
* kame/sys/netinet6/natpt_{dispatch,tslot,var}.[ch]:
- Support translation from ICMPv6 that occurred with IPv6 host
  into ICMPv4 in "IPv4->IPv6" translation.

  This translation is done even if there is no "IPv6->IPv4"
  translation rule, but only this ICMPv6 packet is a target of
  translation.  Because translator examines whether this is
  ICMP of return more first than translation rule, eventually
  "IPv6->IPv4" translation rule is not adapted to.

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