nettest: check what relay candidates can be gathered

[fippo]

the nettest is actually missing a pretty basic test: what relay candidates can be gathered Basically: if you use a turn server and don't get a turn/udp candidate, udp is blocked (or the turn server is down). Same for TCP.

I keep sending [a fiddle for this to customers but it might be actually better to integrate here.

@KaptenJansson we can talk about this when you're back. I just need to know where this would be best to integrate

[KaptenJansson]

The Network checks if it can connect to a turn server using TCP or UDP and get a relay UDP candidate. The Connectivity tests set up a datachannel and tries connect using the different candidate types but all being UDP.

I think it would make sense to add test for both cases, i.e. can we gather candidates vs can we connect using gathered candidates.

[kekkokk]

@fippo It's not clear to me how this works. I mean, reading tests, it says that udp is enabled only if it can connect to the udp turn server and get a relay candidate. but if I simply block 19305 port it says that my udp is blocked. this is not true, only that specific port is blocked, still my traffic would probably flow in another udp port even if the candidate is discovered by a tcp turn server, is that right? Is that what you are saying?

Also, it is not automatic that if I get a candidate I will successfully use it to connect? What might be the factors that prevent it to works? Have a nice day!