iwlwifi: add iwl_sta_id()

In places where the station struct is
guaranteed to exist (presumably), use
this helper to get the station ID out
of it (and warn if there's no station
struct after all).
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>

drivers/net/wireless/iwlwifi/iwl-sta.h

@@ -84,4 +84,12 @@ int iwl_sta_rx_agg_start(struct iwl_priv *priv,
 int iwl_sta_rx_agg_stop(struct iwl_priv *priv, const u8 *addr, int tid);
 void iwl_sta_modify_ps_wake(struct iwl_priv *priv, int sta_id);
 void iwl_sta_modify_sleep_tx_count(struct iwl_priv *priv, int sta_id, int cnt);
+
+static inline int iwl_sta_id(struct ieee80211_sta *sta)
+{
+	if (WARN_ON(!sta))
+		return IWL_INVALID_STATION;
+
+	return ((struct iwl_station_priv_common *)sta->drv_priv)->sta_id;
+}
 #endif /* __iwl_sta_h__ */