publish both IPv4 and IPv6 bridge lines when possible

Solves #40885. Based off !782 so you'll need to handle that one first.

As mentioned in the issue, I'm not happy with how repetitive the code is, but all my attempts to clean it up just made it worse.

It works, though. I've deployed it on one of my bridges, and I started receiving IPv6 connections. I've got confirmation from meskio that both bridge lines are being distributed.