net: Use ip_route_input_noref() in input path

Use ip_route_input_noref() in ip fast path, to avoid two atomic ops per
incoming packet.

Note: loopback is excluded from this optimization in ip_rcv_finish()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 80769f1..f094b75 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -854,7 +854,7 @@
 	}
 
 	if (arp->ar_op == htons(ARPOP_REQUEST) &&
-	    ip_route_input(skb, tip, sip, 0, dev) == 0) {
+	    ip_route_input_noref(skb, tip, sip, 0, dev) == 0) {
 
 		rt = skb_rtable(skb);
 		addr_type = rt->rt_type;