On large mesh WiFi networks where many access points share the same SSID, but are split among multiple LANs/VLANs, SSID-based caching results in unnecessary Cast Channel connection attempts.

This issue tracks work to improve the scalability in these environments.  The items we will be tracking:

1. Incorporate BSSID into the network identifier used to track known Cast devices.
2. Discard disconnected/connecting devices on network id change.
3. Potentially clear all devices on network id change - provided that upstream API's don't see a "blip" in availability while discovery backfills a new set of devices.