If we have gathered a host IP-address that is link-local we should
never try to use it for anything else than trying to match it with
another link-local address. Some routers seem to have problems with
traffic from link-local addresses destined at external IP-addresses.
By definition link-local addresses should stay local so there's no
reason to access STUN/TURN from it or try to form a candidate with
another address that is not link-local.