The actual supplicant state is exposed via a property on the interface
object. So having a separate signal StateChanged for notifying about
changes is a bad idea. The standard PropertiesChanged signal should be
used for this.
The advantage of StateChanged signal was that it includes the previous
state, but not even NetworkManager is making use of this. And tracking
the old state via the property and this signal is easily possible anyway.
Instead of using some magic integer values that really only mean
something to WPA internal code, just use simple strings. Possible
values are "msgdump", "debug", "info", "warning" and "error" which
map directly to WPA debugging support.
In addition, remove Quality and Noise properties since the BSS table
is not the correct place for fetching per-channel information (Noise)
and Quality is not well-defined (nor available from many drivers).
