wrong call to addIceCandidate({}) after timeout

[fippo]

https://jsfiddle.net/qg0njd1s/
apparently runs into the 4 second timeout that tries to run addIceCandidate({})
This should not happen as the SDP has end-of-candidates.

Not very common but would be good to avoid.

[fippo]

the reason this goes wrong is that the 4 second timeout is started in setRemoteDescription but the ice transport is only started in SLD. The right thing is (imo) to move the timeout to where the ice transport is started.

[fippo]

moving this to a function called on start would be eas but the test mock is not complex enough and goes to complete when there is a remote candidate -- instead of waiting for addRemoteCandidate({})