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).
