p54: connect to 11w protected networks

Previously, it was not possible to connect to
networks which requires 11w to be supported by
the stations.

Note:

As all current (and old) firmwares corrupt
incoming, protected management frames, the
decryption offloading needs to be disabled.
This will be done automatically if needed.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>