tcp: add cc stats plotting tools

tcp: add cc stats plotting tools

Type: feature

cc_plot.py can plot cc stats collected via elogs from tcp connections.
To enable the collection of cc stats, tcp must be compiled with
TCP_DEBUG_CC_STAT turned on.

Once the tests have been carried out, and elogs have been saved with "ev
save log <file>", the logs can be converted to txt format with the
convert_evt script. The resulting file can be used as input to the
cc_plots script.

Change-Id: I16df2993fa09cab9ad35f91825eab7df4da6428b
Signed-off-by: Florin Coras <fcoras@cisco.com>