netfilter: gre: Use consistent GRE and PTTP header structure instead of the ones defined by netfilter

There are two existing strutures which defines the GRE and PPTP header.
So use these two structures instead of the ones defined by netfilter to
keep consitent with other codes.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_conntrack_proto_gre.c b/net/netfilter/nf_conntrack_proto_gre.c
index deb239a..9a715f8 100644
--- a/net/netfilter/nf_conntrack_proto_gre.c
+++ b/net/netfilter/nf_conntrack_proto_gre.c
@@ -192,15 +192,15 @@
 static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 			     struct net *net, struct nf_conntrack_tuple *tuple)
 {
-	const struct gre_hdr_pptp *pgrehdr;
-	struct gre_hdr_pptp _pgrehdr;
+	const struct pptp_gre_header *pgrehdr;
+	struct pptp_gre_header _pgrehdr;
 	__be16 srckey;
-	const struct gre_hdr *grehdr;
-	struct gre_hdr _grehdr;
+	const struct gre_base_hdr *grehdr;
+	struct gre_base_hdr _grehdr;
 
 	/* first only delinearize old RFC1701 GRE header */
 	grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
-	if (!grehdr || grehdr->version != ntohs(GRE_VERSION_1)) {
+	if (!grehdr || (grehdr->flags & GRE_VERSION) != GRE_VERSION_1) {
 		/* try to behave like "nf_conntrack_proto_generic" */
 		tuple->src.u.all = 0;
 		tuple->dst.u.all = 0;
@@ -213,7 +213,7 @@
 		return true;
 
 	if (grehdr->protocol != GRE_PROTO_PPP) {
-		pr_debug("GRE_VERSION_PPTP but unknown proto\n");
+		pr_debug("Unsupported GRE proto(0x%x)\n", ntohs(grehdr->protocol));
 		return false;
 	}