Clarify what "available interfaces" means

[fhunleth]

It appears to be a confusing as to what available interfaces means and when you'd want to subscribe to it. For example, if you're starting a server per externally reachable IP address, this property looks interesting since you can start a server when an interface appears in its list. The catch is that IP addresses can change.

I think that the clarification that needs to be added is that if you connect to some place on the internet and don't bind to an interface, then packets go through the first interface in the "available_interfaces" list. Likewise, you should be able to communicate with devices on the LAN on the other interfaces.