netfilter: nf_conntrack: add support for "conntrack zones"

Normally, each connection needs a unique identity. Conntrack zones allow
to specify a numerical zone using the CT target, connections in different
zones can use the same identity.

Example:

iptables -t raw -A PREROUTING -i veth0 -j CT --zone 1
iptables -t raw -A OUTPUT -o veth1 -j CT --zone 1

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/ipv4/netfilter/nf_nat_pptp.c b/net/ipv4/netfilter/nf_nat_pptp.c
index 9eb1710..4c06003 100644
--- a/net/ipv4/netfilter/nf_nat_pptp.c
+++ b/net/ipv4/netfilter/nf_nat_pptp.c
@@ -25,6 +25,7 @@
 #include <net/netfilter/nf_nat_rule.h>
 #include <net/netfilter/nf_conntrack_helper.h>
 #include <net/netfilter/nf_conntrack_expect.h>
+#include <net/netfilter/nf_conntrack_zones.h>
 #include <linux/netfilter/nf_conntrack_proto_gre.h>
 #include <linux/netfilter/nf_conntrack_pptp.h>
 
@@ -74,7 +75,7 @@
 
 	pr_debug("trying to unexpect other dir: ");
 	nf_ct_dump_tuple_ip(&t);
-	other_exp = nf_ct_expect_find_get(net, &t);
+	other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
 	if (other_exp) {
 		nf_ct_unexpect_related(other_exp);
 		nf_ct_expect_put(other_exp);