Chances are that there is a problem with the network hardware or possibly the driver running it. By inserting the cable, it activates the link, which will trigger several software processes.
To be doubly sure, check the console output when you insert the cable to see if anything borks out before the kernel panic.
You can try using a different network card to see if the problem goes away. If it turns out to be a driver problem, using a different version of the kernel or building your own stock kernel might solve the problem.