don't panic if there's no interface address on multicast outgoing interface. sync w/netbsd-current
don't panic if there's no interface address on multicast outgoing interface.
sync w/netbsd-current

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