Support filtering by protocol

[JonathanLennox]

It should be possible to apply a filter to just a single protocol -- e.g., to apply a rule just to TCP or to UDP -- assuming tc proper supports this. (Since it allows filtering by port, I assume it does?)

Use case, for instance: block UDP entirely, so TCP fallback tests for WebRTC can be accomplished.

Protocols should be able to be specified by name (as listed in /etc/protocols, presumably) or by number.

[rainbowflesh]

Any progress?