gre: Fix wrong tpi->proto in WCCP

When dealing with WCCP in gre6 tunnel, it sets the wrong tpi->protocol,
that is, ETH_P_IP instead of ETH_P_IPV6 for the encapuslated traffic.

Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index d78e2ee..4c39f4f 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -62,7 +62,7 @@
 
 /* Fills in tpi and returns header length to be pulled. */
 int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
-		     bool *csum_err)
+		     bool *csum_err, __be16 proto)
 {
 	const struct gre_base_hdr *greh;
 	__be32 *options;
@@ -109,11 +109,11 @@
 		tpi->seq = 0;
 	}
 	/* WCCP version 1 and 2 protocol decoding.
-	 * - Change protocol to IP
+	 * - Change protocol to IPv4/IPv6
 	 * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
 	 */
 	if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
-		tpi->proto = htons(ETH_P_IP);
+		tpi->proto = proto;
 		if ((*(u8 *)options & 0xF0) != 0x40)
 			hdr_len += 4;
 	}