tunnels: prepare percpu accounting

Tunnels are going to use percpu for their accounting.

They are going to use a new tstats field in net_device.

skb_tunnel_rx() is changed to be a wrapper around __skb_tunnel_rx()

IPTUNNEL_XMIT() is changed to be a wrapper around __IPTUNNEL_XMIT()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 01bd4c8..83de0eb 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1053,6 +1053,7 @@
 	union {
 		void				*ml_priv;
 		struct pcpu_lstats __percpu	*lstats; /* loopback stats */
+		struct pcpu_tstats __percpu	*tstats; /* tunnel stats */
 	};
 	/* GARP */
 	struct garp_port	*garp_port;