wifi: mac80211: add ieee80211_tdls_sta_link_id()

We've open-coded this twice and will need it again,
add ieee80211_tdls_sta_link_id() to get the one link
ID for a TDLS STA.
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240612143707.9f8141ae1725.I343822bbba0ae08dedb2f54a0ce87f2ae5ebeb2b@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -727,6 +727,12 @@ struct sta_info {
 	struct ieee80211_sta sta;
 };
 
+static inline int ieee80211_tdls_sta_link_id(struct sta_info *sta)
+{
+	/* TDLS STA can only have a single link */
+	return sta->sta.valid_links ? __ffs(sta->sta.valid_links) : 0;
+}
+
 static inline enum nl80211_plink_state sta_plink_state(struct sta_info *sta)
 {
 #ifdef CONFIG_MAC80211_MESH

net/mac80211/tx.c

@@ -2774,8 +2774,7 @@ static struct sk_buff *ieee80211_build_hdr(struct ieee80211_sub_if_data *sdata,
 
 		if (tdls_peer) {
 			/* For TDLS only one link can be valid with peer STA */
-			int tdls_link_id = sta->sta.valid_links ?
-					   __ffs(sta->sta.valid_links) : 0;
+			int tdls_link_id = ieee80211_tdls_sta_link_id(sta);
 			struct ieee80211_link_data *link;
 
 			/* DA SA BSSID */
@@ -3101,8 +3100,7 @@ void ieee80211_check_fast_xmit(struct sta_info *sta)
 	case NL80211_IFTYPE_STATION:
 		if (test_sta_flag(sta, WLAN_STA_TDLS_PEER)) {
 			/* For TDLS only one link can be valid with peer STA */
-			int tdls_link_id = sta->sta.valid_links ?
-					   __ffs(sta->sta.valid_links) : 0;
+			int tdls_link_id = ieee80211_tdls_sta_link_id(sta);
 			struct ieee80211_link_data *link;
 
 			/* DA SA BSSID */