net: rx_dropped accounting

Under load, netif_rx() can drop incoming packets but administrators dont
have a chance to spot which device needs some tuning (RPS activation for
example)

This patch adds rx_dropped accounting in vlans and tunnels.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 9289cec..f6d9f68 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -725,7 +725,10 @@
 		skb_tunnel_rx(skb, t->dev);
 
 		dscp_ecn_decapsulate(t, ipv6h, skb);
-		netif_rx(skb);
+
+		if (netif_rx(skb) == NET_RX_DROP)
+			t->dev->stats.rx_dropped++;
+
 		rcu_read_unlock();
 		return 0;
 	}
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 66078da..2640c9b 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -666,7 +666,9 @@
 
 	skb_tunnel_rx(skb, reg_dev);
 
-	netif_rx(skb);
+	if (netif_rx(skb) == NET_RX_DROP)
+		reg_dev->stats.rx_dropped++;
+
 	dev_put(reg_dev);
 	return 0;
  drop:
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 6822481..8a03998 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -564,7 +564,10 @@
 		skb_tunnel_rx(skb, tunnel->dev);
 
 		ipip6_ecn_decapsulate(iph, skb);
-		netif_rx(skb);
+
+		if (netif_rx(skb) == NET_RX_DROP)
+			tunnel->dev->stats.rx_dropped++;
+
 		rcu_read_unlock();
 		return 0;
 	}