examples: nft-rule-add: use existing batch infrastructure

This patch reworks the existing example to add the rule:

  nft add rule ip filter input tcp dport 22 counter

It uses the existing nfnl batching approach using the generic mnl
netlink message batching infrastructure. It also removed the code
that uses xtables compat code.

Based on original patch by Arturo Borrero Gonzalez.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
include: update netlink.h to 3.13

Use kernel header from 3.13-rc upstream kernel, this includes
documentation changes that were missing.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>