[NETFILTER]: nf_conntrack: clean up a few header files

- Remove declarations of non-existing variables and functions
- Move helper init/cleanup function declarations to nf_conntrack_helper.h
- Remove unneeded __nf_conntrack_attach declaration and make it static

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
index d7b2d54..2f3af00 100644
--- a/include/net/netfilter/nf_conntrack_helper.h
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -58,4 +58,8 @@
 {
 	return nf_ct_ext_find(ct, NF_CT_EXT_HELPER);
 }
+
+extern int nf_conntrack_helper_init(void);
+extern void nf_conntrack_helper_fini(void);
+
 #endif /*_NF_CONNTRACK_HELPER_H*/