nft: xtables: add the infrastructure to translate from iptables to nft

This patch provides the infrastructure and two new utilities to
translate iptables commands to nft, they are:

1) iptables-restore-translate which basically takes a file that contains
   the ruleset in iptables-restore format and converts it to the nft
   syntax, eg.

 % iptables-restore-translate -f ipt-ruleset > nft-ruleset
 % cat nft-ruleset
 # Translated by iptables-restore-translate v1.4.21 on Mon Apr 14 12:18:14 2014
 add table ip filter
 add chain ip filter INPUT { type filter hook input priority 0; }
 add chain ip filter FORWARD { type filter hook forward priority 0; }
 add chain ip filter OUTPUT { type filter hook output priority 0; }
 add rule ip filter INPUT iifname lo counter accept
 # -t filter -A INPUT -m state --state INVALID -j LOG --log-prefix invalid:
 ...

The rules that cannot be translated are left commented. Users should be able
to run this to track down the nft progress to see at what point it can fully
replace iptables and their filtering policy.

2) iptables-translate which suggests a translation for an iptables
   command:

 $ iptables-translate -I OUTPUT -p udp -d 8.8.8.8 -j ACCEPT
 nft add rule filter OUTPUT ip protocol udp ip dst 8.8.8.8 counter accept

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
10 files changed