mac80211: fix oops on mesh PS broadcast forwarding

Introduced with de74a1d
"mac80211: fix WPA with VLAN on AP side with ps-sta".
Apparently overwrites the sdata pointer with non-valid data in
the case of mesh.
Fix this by checking for IFTYPE_AP_VLAN.

Signed-off-by: Marco Porsch <marco@cozybit.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -2755,7 +2755,8 @@ ieee80211_get_buffered_bc(struct ieee80211_hw *hw,
 				cpu_to_le16(IEEE80211_FCTL_MOREDATA);
 		}
 
-		sdata = IEEE80211_DEV_TO_SUB_IF(skb->dev);
+		if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
+			sdata = IEEE80211_DEV_TO_SUB_IF(skb->dev);
 		if (!ieee80211_tx_prepare(sdata, &tx, skb))
 			break;
 		dev_kfree_skb_any(skb);