[6.9.2] Docker version 20.10.2 through 20.10.5, regression in docker-proxy when using IPv6 with containers in bridge network

This isn't specifically a UnRAID problem but I'm putting it here for visibility and awareness, as UnRAID v6.9.2 is affected by this bug.  

I already commented about the problem over here: UNRAID 6.9.2 - DOCKER CONTAINER NOT REACHABLE OVER THE INTERNET WITH IPV6

There is a problem in the networking engine of Docker when using IPv6 with a container that has only a IPv4 assigned in a bridged network. Prior to Docker version 20.10.2 IPv6 traffic was forwarded to the container regardless. This behavior changed with version 20.10.2. This is the pull request that changed this behavior: Fix IPv6 Port Forwarding for the Bridge Driver 

A fix for this regression was issued 4 days later: Fix regression in docker-proxy but this wasn't implemented into Docker until version 20.10.6.  

For me this is just a minor issue as I have a full dual-stack connection and switched to only IPv4 for now, but for people using a connection via DS-Lite, this could mean that their docker-containers that are operating in bridged mode aren't accessible from outside of their home network anymore (like PLEX or Nextcloud).