socket cheat sheet: AF_INET6 missing

As someone who struggles with finding the right combination of AI_V4MAPPED because he doesn't want to implement things twice for IPv4 and IPv6, I find the lack of AF_INET6 examples disturbing.

IPv4 might not be dead yet, but is on a good way to its sunsetting phase.

Please consider adding IPv6 examples, or even making IPv6 (possibly with V6ONLY=0) the default.