Metrics of glb-director-xdp

We've been using the DPDK glb-director but had issues with driver support, so we're trialling using the XDP implementation instead and first impressions are excellent.

However, the DPDK version had `dpdk-procinfo` and statsd exporting from the `glb-director` process for understanding packets and bytes received and transmitted.

It seems that we can get some semblence of XDP network throughput statistics via `ethtool -S $interface` but it is again driver-specific and doesn't give XDP-only traffic metrics. The [xdp project acknowledges that metrics for XDP are inconsistent at this time](https://github.com/xdp-project/xdp-project/blob/master/xdp-project.org#consistency-for-statistics-with-xdp), and suggests that each XDP program does it's own accounting, [one example of this is given here](https://github.com/xdp-project/xdp-tutorial/tree/master/basic03-map-counter#assignment-1-add-bytes-counter).

Is there already a source of traffic data for glb-director-xdp or would custom solution per the above example be necessary? Is metrics support planned or would it be considered?

Start by tracing how glb-director-xdp currently exposes traffic data, then compare it with the DPDK process's dpdk-procinfo and statsd behavior. Use ethtool -S $interface and the linked XDP map-counter example as reference points. Done means the available source of XDP-only packet and byte metrics, and whether metrics support should be added, are established.

Written by the indexing model from the issue text.