net/ipv4: ip_vti clear skb cb before tunneling.

If users apply shaper to vti tunnel then it will cause a kernel crash. The
problem seems to be due to the vti_tunnel_xmit function not clearing
skb->opt field before passing the packet to xfrm tunneling code.

Signed-off-by: Saurabh Mohan <saurabh@vyatta.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_vti.c

@@ -361,8 +361,7 @@ static netdev_tx_t vti_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 			tunnel->err_count = 0;
 	}
 
-	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
-			      IPSKB_REROUTED);
+	memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 	skb_dst_drop(skb);
 	skb_dst_set(skb, &rt->dst);
 	nf_reset(skb);