Which address should a multi-ORPort Tor put in its "transport" extra-info line?
https://gitweb.torproject.org/torspec.git/blob/HEAD:/dir-spec.txt#l906
When a bridge advertises its pluggable transports to BridgeDB, it adds its external IP address in its "transport" line in its extrainfo descriptor.
We should clearly spec out what a bridge should put in its "transport" line when it has multiple OR addresses.