p54: re-enable power save feature

This patch re-enables p54's power save features and adds a workaround
which temporarily alters the device's power state in order to allow
ps-polls to be sent and buffered data to be retrieved during psm.

(Incorporates patch originally posted as "p54: fix beacon template dtim
IE corruption". -- JWL)

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

drivers/net/wireless/p54/p54.h

@@ -208,6 +208,7 @@ struct p54_common {
 	u32 tsf_low32, tsf_high32;
 	u32 basic_rate_mask;
 	u16 aid;
+	bool powersave_override;
 	__le32 beacon_req_id;
 
 	/* cryptographic engine information */