Add a mode non-configuration leaf per instance on snabb-softwire-v2

[tsyesika]

Currently there is no good way to know how an instance is configured. One can partially deduce it based on if it has a device in the external-interface container of the instance however it doesn't account for virtio configurations.

I think it'd be fairly easy to add a state data leaf to the queue element which specifies what configuration it's using. I think it'd be useful information for debugging and possibly for operators but also for tests so we can query what mode it's using when we add an instance.

Schema change below:

enumeration RunningMode {
  enum OnAStick {
    description "Using a single NIC for INET-side and B4-side."
  }
  enum BumpInTheWire {
    description "Using two NIC, one for INET traffic and one for B4 traffic.";
  }
  enum Virtio {
    description "Using the virtio-net interfaces instead of Intel 82599."
  }
}

...

list queue {
  ...

  leaf running-mode {
    type RunningMode;
    config false;
    description "The mode the instance is running in.";
  }
}

WDYT @wingo?

[wingo]

For virtio, since virtio also comes from a PCI address, I feel like it would be nice to be able to just detect when the configured device is virtio or not. I.e. setup.lua takes the conf and just does whatever is necessary. I get what you're saying but am a little hesitant to add a config (or even state!) option that might be redundant.

At the same time I do see where it would be nice to add a state leaf indicating the driver that was chosen for a device! Probably after our next milestone though; wdyt?