scenario where an anycast address is assigned on one interface,
and a global address with the same scope is assigned on another
interface. In other words, the interface owns the anycast
address has only the link-local address as one other address.
Without this patch, "ping6" the anycast address from another
station will observe the source address of the returned ICMP6
echo reply has the link-local address, not the global address
that exists on the other interface in the same node.
Reviewed by: bz
MFC after: immediately