This plugin tracks the occupation of the shared medium (wifi channel).
It uses the "iw" tool for extracting the time slices spent by
the wireless driver receiving, transmitting or ignoring (noise) on the
current channel. This ratio is a good indication for the remaining
capacity of the shared communication medium.
Reset the error mode of Net::Telnet to 'return', so that we can (try to)
log out during the error handler without invoking the error handler
(doing so resulted in "Deep Recursion" warnings from perl).
Also, return 'U' for ALL appropriate items in case of error.