wifi: mac80211: always initialize link_sta with sta

When we have multiple interfaces receiving the same frame,
such as a multicast frame, one interface might have a sta
and the other not. In this case, link_sta would be set but
not cleared again.

Always set link_sta, so we keep an invariant that link_sta
and sta are either both set or both not set.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -4125,6 +4125,8 @@ static bool ieee80211_rx_data_set_sta(struct ieee80211_rx_data *rx,
 		if (!rx->sdata)
 			rx->sdata = sta->sdata;
 		rx->link_sta = &sta->deflink;
+	} else {
+		rx->link_sta = NULL;
 	}
 
 	if (link_id < 0)