geneve: fix ip_hdr_len reserved for geneve6 tunnel.

It shold reserved sizeof(ipv6hdr) for geneve in ipv6 tunnel.

Fixes: c3ef5aa5e5 ('geneve: Merge ipv4 and ipv6 geneve_build_skb()')
Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/geneve.c

@@ -852,7 +852,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 					   ip_hdr(skb), skb);
 		ttl = key->ttl ? : ip6_dst_hoplimit(dst);
 	}
-	err = geneve_build_skb(dst, skb, info, xnet, sizeof(struct iphdr));
+	err = geneve_build_skb(dst, skb, info, xnet, sizeof(struct ipv6hdr));
 	if (unlikely(err))
 		return err;