QEMU/KVM IPv6 Support

Overview
You have rented a whole server in a data centre somewhere and are running a few Kernel Virtual Machines (KVMs). Your provider gives you a single IPv4 address and a IPv6 /64 subnet. Its a nusciance to use IPv4 with non stanadard ports on the KVMs and you are too parsimonious to invest in more IPv4 addresses, its a hobby server after all. You get a single IPv4 address and a whole IPv6 /64 subnet, since your provider cannot give you any less.

Lets put the KVMs onto IPv6 so that they have global scope IPv6 addresses.