- Fix a bug that ipv6->ip6_plen has wrong value when ipv4 header has   optional field.
- Fix a bug that ipv6->ip6_plen has wrong value when ipv4 header has
  optional field.

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