p54: deactivate broken powersave function (part 2)

This patch deactivates powersave in station mode.

It does not work correctly yet, so the code does more harm than good.

(I split the original patch and sent part of it for 2.6.30, which didn't
have the IEEE80211_HW_BEACON_FILTER flag. -- JWL)

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>