[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables

This monster-patch tries to do the best job for unifying the data
structures and backend interfaces for the three evil clones ip_tables,
ip6_tables and arp_tables.  In an ideal world we would never have
allowed this kind of copy+paste programming... but well, our world
isn't (yet?) ideal.

o introduce a new x_tables module
o {ip,arp,ip6}_tables depend on this x_tables module
o registration functions for tables, matches and targets are only
  wrappers around x_tables provided functions
o all matches/targets that are used from ip_tables and ip6_tables
  are now implemented as xt_FOOBAR.c files and provide module aliases
  to ipt_FOOBAR and ip6t_FOOBAR
o header files for xt_matches are in include/linux/netfilter/,
  include/linux/netfilter_{ipv4,ipv6} contains compatibility wrappers
  around the xt_FOOBAR.h headers

Based on this patchset we're going to further unify the code,
gradually getting rid of all the layer 3 specific assumptions.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/ipv4/nf_conntrack_ipv4.h

@@ -37,7 +37,4 @@ struct nf_conntrack_ipv4 {
 struct sk_buff *
 nf_ct_ipv4_ct_gather_frags(struct sk_buff *skb);
 
-/* call to create an explicit dependency on nf_conntrack_l3proto_ipv4. */
-extern void need_ip_conntrack(void);
-
 #endif /*_NF_CONNTRACK_IPV4_H*/

include/net/netfilter/nf_conntrack.h

@@ -221,9 +221,6 @@ extern void nf_ct_helper_put(struct nf_conntrack_helper *helper);
 extern struct nf_conntrack_helper *
 __nf_conntrack_helper_find_byname(const char *name);
 
-/* call to create an explicit dependency on nf_conntrack. */
-extern void need_nf_conntrack(void);
-
 extern int nf_ct_invert_tuplepr(struct nf_conntrack_tuple *inverse,
 				const struct nf_conntrack_tuple *orig);