[NETFILTER]: nf_conntrack: /proc compatibility with old connection tracking

This patch adds /proc/net/ip_conntrack, /proc/net/ip_conntrack_expect and
/proc/net/stat/ip_conntrack files to keep old programs using them working.

The /proc/net/ip_conntrack and /proc/net/ip_conntrack_expect files show only
IPv4 entries, the /proc/net/stat/ip_conntrack shows global statistics.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/netfilter/nf_conntrack_l3proto_generic.c b/net/netfilter/nf_conntrack_l3proto_generic.c
index 3124b3a..a3d31c3 100644
--- a/net/netfilter/nf_conntrack_l3proto_generic.c
+++ b/net/netfilter/nf_conntrack_l3proto_generic.c
@@ -92,3 +92,4 @@
 	.prepare	 = generic_prepare,
 	.get_features	 = generic_get_features,
 };
+EXPORT_SYMBOL_GPL(nf_conntrack_l3proto_generic);