ip6_gre: Fix a bug that clears address bits

In compatible gre module, skb->cb is solely used as ovs_gso_cb.
However, IPCB(skb) also points to skb->cb. IPCB(skb)->flags overlaps
with ovs_gso_cb.tun_dst. As a result, this bug clears the 16-23 bit
in the address of ovs_gso_cb.tun_dst and causes kernel to crash.

Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Tested-by: Greg Rose <gvrose8192@gmail.com>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>

datapath/linux/compat/ip6_gre.c

@@ -876,9 +876,6 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
 	struct tnl_ptk_info tpi;
 	__be16 protocol;
 
-	if (dev->type == ARPHRD_ETHER)
-		IPCB(skb)->flags = 0;
-
 	if (dev->header_ops && dev->type == ARPHRD_IP6GRE)
 		fl6->daddr = ((struct ipv6hdr *)skb->data)->daddr;
 	else
@@ -1146,7 +1143,6 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 		goto tx_err;
 
 	t->parms.o_flags &= ~TUNNEL_KEY;
-	IPCB(skb)->flags = 0;
 
 	tun_info = ovs_skb_tunnel_info(skb);
 	if (unlikely(!tun_info ||