[colug-432] tracking WAN data usage

[Scott Merrill]

> I have an extra pi, I was thinking of maybe having pfSense ship the stats
> to that. Is there a better tool than ntop? Even if the only stats I got
> were total data used, and maybe total (WAN?) data used by device - I
> think
> that might be good enough.

I've been using rrdtool to track and graph the interface statistics on
my Asus router.

Originally, I simply had a Python script that would telnet into my
router and parse the output of `ifconfig`.  This worked, but wasn't
awesome.  I later enabled SNMP on my router using this:
   http://daniel.abbatt.net/2014/11/enabling-snmp-on-asus-rt-n66u.html

I also run a speedtest every four hours (plus a random number of
seconds, up to 30 minutes) and record those results, so that I can see
if I'm getting close to what I'm paying for.  I just pushed this code to
GitHub: https://github.com/skpy/speedtest-rrd