* sys/netinet6/ip6_mroute.[ch]: add backward compatibility code with   for 2000/4/12 mrt6msg change (is not used in kame tree).   freebsd40 and openbsd27 are shipped with old declaration, so we   need to provide backward compat to some degree.
* sys/netinet6/ip6_mroute.[ch]: add backward compatibility code with
  for 2000/4/12 mrt6msg change (is not used in kame tree).
  freebsd40 and openbsd27 are shipped with old declaration, so we
  need to provide backward compat to some degree.

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