[PATCH] libertas: make debug configurable

The debug output of libertas was either not present or it was overwhelming.
This patch adds the possibility to specify a bitmask for the area of
interest. One should then only get the desired output.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>