Browser to browser connectivity not established with IPv6

When using IPv6 addresses by default, I that observe two browser nodes A and B are both able to establish a webrtc-direct connection to the relay node but neither a relayed connection nor a subsequent webrtc connection to one another.
This functionality works when using IPv4 with no other changes.

Start by reproducing browser-to-browser connectivity with IPv6 and compare the result with the working IPv4 scenario. Trace the relay and subsequent peer-connection setup to identify where IPv6 connectivity stops; done means both browser nodes establish the expected relayed or direct connection over IPv6.

Written by the indexing model from the issue text.