Proper IPv6 Support

[Hugo54x]

Tell us about your request
The main problem with the improper IPv6 support is, that it is completly unusable on networks with non-static ipv6 global addresses

Which service(s) is this request for?
docker engine

Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?
Docker is NATting host addresses, e.g. 192.168.0.0/16 to the internal services subnet 172.x.x.x. Both are these including 10.0.0.0/8 are local useable subnets. In IPv6 this exact same thing exists called ULA (Unique Local Addresses: fd00::/8). These addresses are purely local and can be static, which is great for local testing, as the global prefix (first part of the 2003 addresses, which might be /56 or /62, ...) may change depending on your ISP. If your deploying a kind Kubernetes cluster and enable IPv6, the default IPv6 address pool is the ULA space. Problem is, that it cannot communicate with external services like e.g. Github, as the container has no 2003 address. Using only global addresses is also not the best, as when the prefix changes you do not know your ipv6 address to connect to the service anymore. Yes, you can set DNS entries for that or utilize something like PfSense/OpenSense, but in daily business I haven't seen any company that utilizes this.

Are you currently working around the issue?
No, this problem is a real showstopper. Take a look at the ticket in docker swarm which also heavily suffers from that issue

Additional context
Add any other context or screenshots about the feature request here.