changing interface results in broken graphs

[mglb1]

When a madwifi based interface is taken down and up again the graphs break and record ridiculous traffic values like 100Mbps.

This should be fixed, there are several complementary approaches, which are used by other graping tools like MRTG, Cacti, etc

1. Implement a limit for each class, eg, an 802.11b wireless interface should never do more than 11Mbps of traffic, and so on
2. Check for wraps in the counter and handle appropriately, you can probably look at how MRTG and Cacti handle this.