Circuit Relay v2 should not publish routing key without public addresses

[achingbrain]

If a node has no publicly diallable non-relay addresses it shouldn't publish a provider record saying it is a circuit relay server, much like kad-dht requires public addresses to become a server.

The JS implementation may not do this, but it needs double-checking because I think I saw a provider record for a JS peer that only had relay addresses.

[achingbrain]

Closing in favour of #2545