[NETFILTER]: nf_nat: add symbolic dependency on IPv4 conntrack

Loading nf_nat causes the conntrack core to be loaded, but we need IPv4 as
well.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/ipv4/nf_conntrack_ipv4.h

@@ -21,4 +21,6 @@ extern struct nf_conntrack_l4proto nf_conntrack_l4proto_icmp;
 extern int nf_conntrack_ipv4_compat_init(void);
 extern void nf_conntrack_ipv4_compat_fini(void);
 
+extern void need_ipv4_conntrack(void);
+
 #endif /*_NF_CONNTRACK_IPV4_H*/

net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c

@@ -509,3 +509,9 @@ static void __exit nf_conntrack_l3proto_ipv4_fini(void)
 
 module_init(nf_conntrack_l3proto_ipv4_init);
 module_exit(nf_conntrack_l3proto_ipv4_fini);
+
+void need_ipv4_conntrack(void)
+{
+	return;
+}
+EXPORT_SYMBOL_GPL(need_ipv4_conntrack);

net/ipv4/netfilter/nf_nat_standalone.c

@@ -328,7 +328,7 @@ static int __init nf_nat_standalone_init(void)
 {
 	int ret = 0;
 
-	need_conntrack();
+	need_ipv4_conntrack();
 
 #ifdef CONFIG_XFRM
 	BUG_ON(ip_nat_decode_session != NULL);