sockaddr_in6 is in http://pubs.opengroup.org/onlinepubs/000095399/basedefs/netinet/in.h.html
linux getifaddrs: http://man7.org/linux/man-pages/man3/getifaddrs.3.html
freebsd getifaddrs: http://www.freebsd.org/cgi/man.cgi?query=getifaddrs
u/g bits (iids): https://tools.ietf.org/html/rfc7136
stable privacy addresses: http://tools.ietf.org/html/draft-ietf-6man-stable-privacy-addresses
ULA prefix fc00::/7 http://tools.ietf.org/html/rfc4193#section-8