Update to RFC 3484 Default Address Selection for IPv6

RFC 3484 has several known issues to be fixed. Deprecation of IPv6 site-local unicast address and the coming of ULA brought some preferable changes to the rules. Additionally, the rule 9 of the destination address selection rules, namely the longest matching rule, is known for its adverse effect on the round robin DNS technique. This document covers these points to be fixed and proposes possible useful changes to be included in the revision of RFC 3484.