mt76: mt76x02: add check for invalid vif idx

On adding vifs the idx can become 1 + (7 & 7) = 8 for APs.
Check against that, as only AP vif idx 0-7 is possible.
Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76x02_util.c

@@ -325,7 +325,9 @@ mt76x02_add_interface(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
 	if (vif->type == NL80211_IFTYPE_STATION)
 		idx += 8;
 
-	if (dev->vif_mask & BIT(idx))
+	/* vif is already set or idx is 8 for AP/Mesh/... */
+	if (dev->vif_mask & BIT(idx) ||
+	    (vif->type != NL80211_IFTYPE_STATION && idx > 7))
 		return -EBUSY;
 
 	dev->vif_mask |= BIT(idx);