ath9k: fix race with IEEE80211_CONF_PS checks

There is a small window where the mac80211 changes the IEEE80211_CONF_PS
flag, and then informs the driver about the change. We have a race
condition if we are checking the flag in the same time. Avoid it by
introducing a local variable, and using that instead of checking the
IEEE80211_CONF_PS flag directly.

This fix the problem reported by Luis:
http://article.gmane.org/gmane.linux.kernel.wireless.general/34363

Changes-licensed-under: ISC
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
index e2ebf1a..3a978bf 100644
--- a/drivers/net/wireless/ath/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath/ath9k/ath9k.h
@@ -573,6 +573,7 @@
 	u32 keymax;
 	DECLARE_BITMAP(keymap, ATH_KEYMAX);
 	u8 splitmic;
+	bool ps_enabled;
 	unsigned long ps_usecount;
 	enum ath9k_int imask;
 	enum ath9k_ht_extprotspacing ht_extprotspacing;