Prep work for ReceiverSatellite, call BasePool callback for discovered services on start

Some commits from !390 (merged) that can already be included.

In particular, this includes a vital fix for the BasePool: when start() is called, it only calls the callback to connect to the socket for newly discovered CHIRP services. However, when a service is already discovered, the BasePool never connects to it. To fix this, we call the callback for all already discovered services.