So we can make the panic mode module removal fail, for the "MAC
addresse spoofing fails and the module is not removed" scenario.

Some hardware fails to report the permanent MAC address for
`macchanger -p`. To deal with it we simply record the MAC address
before and after trying to spoof it, and compare them. However, since
macchanger truly picks a random value, it can randomly pick the real
MAC address so there's a 1/2^24 probability that nothing really fails
but the fail safe will trigger any way.

We could migrate to ip instead, but it isn't suitable for these
particular tasks. The sysfs interface makes it all very clean.

It wasn't very robust any way, so let's implement it properly in the
future if we need it.