batman-adv: linearise the tt_response skb only if needed

The TT_RESPONSE skb has to be linearised only if the node plans to access the
packet payload (so only if the message is directed to that node). In all the
other cases the node can avoid this memory operation
Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/routing.c

@@ -616,13 +616,14 @@ int recv_tt_query(struct sk_buff *skb, struct hard_iface *recv_if)
 		}
 		break;
 	case TT_RESPONSE:
-		/* packet needs to be linearized to access the TT changes */
-		if (skb_linearize(skb) < 0)
-			goto out;
+		if (is_my_mac(tt_query->dst)) {
+			/* packet needs to be linearized to access the TT
+			 * changes */
+			if (skb_linearize(skb) < 0)
+				goto out;
 
-		if (is_my_mac(tt_query->dst))
 			handle_tt_response(bat_priv, tt_query);
-		else {
+		} else {
 			bat_dbg(DBG_TT, bat_priv,
 				"Routing TT_RESPONSE to %pM [%c]\n",
 				tt_query->dst,