- fixed a bug that we can't send a packet to ipv4mapped ipv6 address   using a udp6 socket without bind(2)ing. - fbsd4/430 reported from the FreeBSD team. - this fix is different from the fix reported in the above PR.  i think   this better, but we need some test.
- fixed a bug that we can't send a packet to ipv4mapped ipv6 address
  using a udp6 socket without bind(2)ing.
- fbsd4/430 reported from the FreeBSD team.
- this fix is different from the fix reported in the above PR.  i think
  this better, but we need some test.

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