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/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index e310f15..24a42ef 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -26,6 +26,7 @@
 #include <net/netfilter/nf_conntrack_expect.h>
 #include <net/netfilter/nf_conntrack_helper.h>
 #include <net/netfilter/nf_conntrack_acct.h>
+#include <net/netfilter/nf_conntrack_zones.h>
 
 MODULE_LICENSE("GPL");
 
@@ -171,6 +172,11 @@
 		goto release;
 #endif
 
+#ifdef CONFIG_NF_CONNTRACK_ZONES
+	if (seq_printf(s, "zone=%u ", nf_ct_zone(ct)))
+		goto release;
+#endif
+
 	if (seq_printf(s, "use=%u\n", atomic_read(&ct->ct_general.use)))
 		goto release;