Add API for checking whether a peer is connected through a relay server

[johanhelsing]

I want this because I want to tell my players why their latency is bad.

It looks hairy, but doable. Not sure what the API will be.

[simbleau]

I'm just curious, but why not just an API to negotiate ping to a specific peer?

Ideally without needing to negotiate the answer/offer first! I want to tell users the best servers (peers) by ping on a world list before they connect.

I currently do this with an HTTP call, which has overhead and isn't representative of p2p ping.

[johanhelsing]

Ideally, we'd have ping available through the same API, but not critical for me, as I already get it through ggrs.