netfilter: nf_conntrack: push zone object into functions

This patch replaces the zone id which is pushed down into functions
with the actual zone object. It's a bigger one-time change, but
needed for later on extending zones with a direction parameter, and
thus decoupling this additional information from all call-sites.

No functional changes in this patch.

The default zone becomes a global const object, namely nf_ct_zone_dflt
and will be returned directly in various cases, one being, when there's
f.e. no zoning support.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_conntrack_pptp.c b/net/netfilter/nf_conntrack_pptp.c
index 825c3e3..5588c7a 100644
--- a/net/netfilter/nf_conntrack_pptp.c
+++ b/net/netfilter/nf_conntrack_pptp.c
@@ -143,13 +143,14 @@
 				  const struct nf_conntrack_tuple *t)
 {
 	const struct nf_conntrack_tuple_hash *h;
+	const struct nf_conntrack_zone *zone;
 	struct nf_conntrack_expect *exp;
 	struct nf_conn *sibling;
-	u16 zone = nf_ct_zone(ct);
 
 	pr_debug("trying to timeout ct or exp for tuple ");
 	nf_ct_dump_tuple(t);
 
+	zone = nf_ct_zone(ct);
 	h = nf_conntrack_find_get(net, zone, t);
 	if (h)  {
 		sibling = nf_ct_tuplehash_to_ctrack(h);