net: Introduce skb_tunnel_rx() helper

skb rxhash should be cleared when a skb is handled by a tunnel before
being delivered again, so that correct packet steering can take place.

There are other cleanups and accounting that we can factorize in a new
helper, skb_tunnel_rx()

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 2599870..8f39893 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -723,14 +723,10 @@
 		skb->protocol = htons(protocol);
 		skb->pkt_type = PACKET_HOST;
 		memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
-		skb->dev = t->dev;
-		skb_dst_drop(skb);
-		nf_reset(skb);
+
+		skb_tunnel_rx(skb, t->dev);
 
 		dscp_ecn_decapsulate(t, ipv6h, skb);
-
-		t->dev->stats.rx_packets++;
-		t->dev->stats.rx_bytes += skb->len;
 		netif_rx(skb);
 		rcu_read_unlock();
 		return 0;