xtables: bootstrap ARP compatibility layer for nftables

This patch bootstraps ARP support for the compatibility layer:

1) copy original arptables code into xtables-arp.c
2) adapt it to fit into the existing nft infrastructure.
3) add the builtin table/chains for ARP.
4) add necessary parts so xtables-multi can provide xtables-arp.
5) add basic support for rule addition (-A), insertion (-I) and
   listing (-L).

[ This was originally posted in a series of patches with interdependencies
  that I have collapsed to leave the repository in consistent state. This
  patch includes the following changes I made:

* Rename from xtables-arptables to xtables-arp, previous name too long.
* Remove nft-arptables.c, now we have one single nft-arp.c file. Moved
  specific ARP functions to nft.c. Those should go away at some point as
  some refactorization should allow to accomodate those functions to the
  existing infrastructure.
* Fix --opcode Request/Reply, so we can do something useful with this
  like dropping ARP request/replies.

--pablo ]

Signed-off-by: Giuseppe Longo <giuseppelng@gmail.com>
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
11 files changed