[NETFILTER]: nf_nat: add reference to conntrack from entry of bysource list

I will split 'struct nf_nat_info' out from conntrack. So I cannot use
'offsetof' to get the pointer to conntrack from it.

Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/nf_nat.h

@@ -53,11 +53,14 @@ struct nf_nat_multi_range_compat
 #include <linux/list.h>
 #include <linux/netfilter/nf_conntrack_pptp.h>
 
+struct nf_conn;
+
 /* The structure embedded in the conntrack structure. */
 struct nf_nat_info
 {
 	struct list_head bysource;
 	struct nf_nat_seq seq[IP_CT_DIR_MAX];
+	struct nf_conn *ct;
 };
 
 /* per conntrack: nat application helper private data */
@@ -77,8 +80,6 @@ struct nf_conn_nat
 #endif
 };
 
-struct nf_conn;
-
 /* Set up the info structure to map into this range. */
 extern unsigned int nf_nat_setup_info(struct nf_conn *ct,
 				      const struct nf_nat_range *range,