netfilter: nf_ct_helper: implement variable length helper private data

This patch uses the new variable length conntrack extensions.

Instead of using union nf_conntrack_help that contain all the
helper private data information, we allocate variable length
area to store the private helper data.

This patch includes the modification of all existing helpers.
It also includes a couple of include header to avoid compilation
warnings.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/ipv4/netfilter/nf_nat_pptp.c b/net/ipv4/netfilter/nf_nat_pptp.c
index c273d58..3881408 100644
--- a/net/ipv4/netfilter/nf_nat_pptp.c
+++ b/net/ipv4/netfilter/nf_nat_pptp.c
@@ -49,7 +49,7 @@
 	const struct nf_nat_pptp *nat_pptp_info;
 	struct nf_nat_ipv4_range range;
 
-	ct_pptp_info = &nfct_help(master)->help.ct_pptp_info;
+	ct_pptp_info = nfct_help_data(master);
 	nat_pptp_info = &nfct_nat(master)->help.nat_pptp_info;
 
 	/* And here goes the grand finale of corrosion... */
@@ -123,7 +123,7 @@
 	__be16 new_callid;
 	unsigned int cid_off;
 
-	ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
+	ct_pptp_info = nfct_help_data(ct);
 	nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 
 	new_callid = ct_pptp_info->pns_call_id;
@@ -192,7 +192,7 @@
 	struct nf_ct_pptp_master *ct_pptp_info;
 	struct nf_nat_pptp *nat_pptp_info;
 
-	ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
+	ct_pptp_info = nfct_help_data(ct);
 	nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 
 	/* save original PAC call ID in nat_info */