Fixed a transient error discovered by Junxing. Rather, I've fixed a bug that could account for it and the error hasn't resurfaced after many runs. The transient symptom was when pcap only captured the first three packets and failed from then on.

All measurement times are now based on packet timestamps rather than gettimeofday(), throughput measurement is much more consistent now, though a more thorough evaluation is still required.

Delay is averaged over a quantum. This is probably not the right thing to do, but it is better than the alternative (latest measurement). I am still discussion with Sneha about what to do here.