The webrtc-stats spec defines this field as:
> It is the protocol used by the endpoint to communicate with the TURN
> server. This is only present for local candidates. Valid values are
> "udp", "tcp", or "tls".
https://w3.org/TR/webrtc-stats/#dom-rtcicecandidatestats-relayprotocol
Callers of run need to be able to cancel their waiting individually.
This would cause hung threads during restart if we attempted to close
a candidate while processing a packet for it.
Before the run would be canceled by the global close, but we can't
depend on that anymore.
Resolves#190
