[Cake] drop graph plotting

[Dave Taht]

>From analysis of packet captures it is not hard to recognise ecn
marks, but very difficult to infer when packets are dropped.

The drop graph from cake_drop_monitor could be vertically (identified
flows), over time horizontally (showing drops/ecn amarks)

As well as doing elephant/mice plotting as I was showing in my early
presos on fq_codel, as a desirable graph to have. Don't have the
reference on elephant and mice flow paper handy....

-- 
Dave Täht
Open Networking needs **Open Source Hardware**

https://plus.google.com/u/0/+EricRaymond/posts/JqxCe2pFr67