firewall: specify interfaces for rules explicitly.

When `firewall` was first written, all of the network interfaces on a
Network Box were either ephemeral (GFiberSetup) or trusted, and implying
them seemed like a good idea at the time.

This isn't true any more; both autoprovisioning networks and Fiber
Managed WiFi serve fundamentally untrusted devices, and need to isolate
them from mutually trusting devices on the private network.

Fixes b/33678893, b/31933763.

Change-Id: I403ddb9ad754a6c88cbe3a5e0b3608c915ff226e
1 file changed