my munin-surfboard6120 updates (if you wish to pull them in)

Hello Jeff,

First, thanks for providing your munin-surfboard6120 source code on github!  I decided to fork your script in order to modify it a bit to support multiple graphs (one for the SNR, one for the signal strengths, and one for the uptime of the surfboard).  I also am using it for my Surfboard 6141 instead of the 6120 (for a few days now), and I believe all my changes would probably work for a 6120.  Anyway, I just wanted to let you know about my fork in case you wished to pull in the changes or if you had any interest in my updates.

Thanks again for providing the original script!

- David Reitz