[Ecn-sane] results of two simple ECN tests

[Dave Taht]

I appreciate the shot at going back to basics and the packet capture
driven tests.

ECN does help keep latency down at longer RTTs. But the bandwidth
improvements are rather minimal in this test case, and basically a
function of what would have been the drop rate. The pathological cases
I was discussing at one point (100 flows through a short low bandwidth
link) dramatically increase delay, cause starvation for other flows
(including new flows trying to start).