Maybe use "has authenticated" rather than "has authenticated as a known relay" to set client flag
In legacy/trac#22805 (moved), teor proposes that we should use the following rule for setting our "is this a client flag" on a channel:
If a connecting peer has a zero identity digest, it's a client/bridge, if it doesn't, it's a relay. (A listening peer is always a relay. Interestingly, bridges look like relays to clients, but look like clients to public relays.)