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/ip6mr.c b/net/ipv6/ip6mr.c
index 163850e..bd9e7d3 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -658,14 +658,12 @@
 	skb->mac_header = skb->network_header;
 	skb_pull(skb, (u8 *)encap - skb->data);
 	skb_reset_network_header(skb);
-	skb->dev = reg_dev;
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->ip_summed = 0;
 	skb->pkt_type = PACKET_HOST;
-	skb_dst_drop(skb);
-	reg_dev->stats.rx_bytes += skb->len;
-	reg_dev->stats.rx_packets++;
-	nf_reset(skb);
+
+	skb_tunnel_rx(skb, reg_dev);
+
 	netif_rx(skb);
 	dev_put(reg_dev);
 	return 0;