iwlwifi: optimize power saving

In hostap AP mode, every time the client sends the AP
a packet the STA_NOTIFY_AWAKE code is sent from mac80211.
This results in a command being sent to the uCode even if
the client was not asleep.

The following simple patch has fixed the issue for me without any
degradation that I can find.
Signed-off-by: NDaniel Halperin <dhalperi@cs.washington.edu>
Acked-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NReinette Chatre <reinette.chatre@intel.com>

drivers/net/wireless/iwlwifi/iwl-agn.c

@@ -3007,6 +3007,8 @@ static void iwl_mac_sta_notify(struct ieee80211_hw *hw,
 		break;
 	case STA_NOTIFY_AWAKE:
 		WARN_ON(!sta_priv->client);
+		if (!sta_priv->asleep)
+			break;
 		sta_priv->asleep = false;
 		sta_id = iwl_find_station(priv, sta->addr);
 		if (sta_id != IWL_INVALID_STATION)