s/ip6_hdr/ip6/ (readability) more sanity check on parsing ip4 header.
s/ip6_hdr/ip6/ (readability)
more sanity check on parsing ip4 header.

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