mac80211: don't re-init rate control when receiving mesh beacon

Rate control is re-initialized whenever a beacon from a mesh
peer received, breaking the algorithms and resulting in low
performance. Return early from mesh_peer_init if we already
established a link with this peer to avoid this.
Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
[clarify commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mesh_plink.c

@@ -362,6 +362,11 @@ static struct sta_info *mesh_peer_init(struct ieee80211_sub_if_data *sdata,
 
 	spin_lock_bh(&sta->lock);
 	sta->last_rx = jiffies;
+	if (sta->plink_state == NL80211_PLINK_ESTAB) {
+		spin_unlock_bh(&sta->lock);
+		return sta;
+	}
+
 	sta->sta.supp_rates[band] = rates;
 	if (elems->ht_cap_elem &&
 	    sdata->local->_oper_channel_type != NL80211_CHAN_NO_HT)