ip6_udp_tunnel: remove unused IPCB related codes

Some IPCB fields are currently set in udp_tunnel6_xmit_skb(), which are
never used before it reaches ip6tunnel_xmit(), and past that point the
control buffer is no longer interpreted as IPCB.

This clears these unused IPCB related codes. Currently there is no skb
scrubbing in ip6_udp_tunnel, otherwise IPCB(skb)->opt might need to be
cleared for IPv4 packets, as shown in 5146d1f1
("tunnel: Clear IPCB(skb)->opt before dst_link_failure called").
Signed-off-by: NEli Cooper <elicooper@gmx.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_udp_tunnel.c

@@ -88,9 +88,6 @@ int udp_tunnel6_xmit_skb(struct dst_entry *dst, struct sock *sk,
 
 	uh->len = htons(skb->len);
 
-	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
-	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED
-			    | IPSKB_REROUTED);
 	skb_dst_set(skb, dst);
 
 	udp6_set_csum(nocheck, skb, saddr, daddr, skb->len);