device: prefer IPv6 not-deprecated addresses for hostname lookup

(the branch is 4 commits, on top of bg/resolve-helper)

In presence of a IPv6 deprecated address and a non-deprecated one, the non-deprecated address will be used for new connections, according to RFC 6724 section 5 (Source Address Selection). Prefer it also to lookup a hostname via reverse DNS.

While at it, also prefer non-link-local addresses over link-local ones.