New congestion control metrics
@dgoulet and I are puzzling over why the average congestion control window is hovering around 400 on our test relays: tpo/network-health/analysis#44 (comment 2857941)
We're going to add at least 3-4 more metrics to help diagnose this:
- queue use
- Vegas BDP
- number of circuits that exit slow start
- Percent of circuits that exit slow start