ipv4: ip_forward: perform skb->pkt_type check at the beginning

Packets which have L2 address different from ours should be
already filtered before entering into ip_forward().

Perform that check at the beginning to avoid processing such packets.
Signed-off-by: NDenis Kirjanov <kda@linux-powerpc.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_forward.c

@@ -59,6 +59,10 @@ int ip_forward(struct sk_buff *skb)
 	struct rtable *rt;	/* Route we use */
 	struct ip_options *opt	= &(IPCB(skb)->opt);
 
+	/* that should never happen */
+	if (skb->pkt_type != PACKET_HOST)
+		goto drop;
+
 	if (skb_warn_if_lro(skb))
 		goto drop;
 
@@ -68,9 +72,6 @@ int ip_forward(struct sk_buff *skb)
 	if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
 		return NET_RX_SUCCESS;
 
-	if (skb->pkt_type != PACKET_HOST)
-		goto drop;
-
 	skb_forward_csum(skb);
 
 	/*