extensions: libipt_DNAT: Add translation to nft

extensions: libipt_DNAT: Add translation to nft

Add translation for target DNAT to nftables.

Examples:

$ sudo iptables-translate -t nat -A prerouting -p tcp -o eth0 -j DNAT --to-destination 1.2.3.4
nft add rule ip nat prerouting oifname eth0 ip protocol tcp counter dnat 1.2.3.4

$ sudo iptables-translate -t nat -A prerouting -p tcp -d 15.45.23.67 --dport 80 -j DNAT --to-destination 192.168.1.1-192.168.1.10
nft add rule ip nat prerouting ip daddr 15.45.23.67 tcp dport 80 counter dnat 192.168.1.1-192.168.1.10

$ sudo iptables-translate -t nat -A prerouting -p tcp -o eth0 -j DNAT --to-destination 1.2.3.4:1-1023
nft add rule ip nat prerouting oifname eth0 ip protocol tcp counter dnat 1.2.3.4:1-1023

$ sudo iptables-translate -t nat -A prerouting -p tcp -o eth0 -j DNAT --to-destination 1.2.3.4 --random
nft add rule ip nat prerouting oifname eth0 ip protocol tcp counter dnat 1.2.3.4 random

$ sudo iptables-translate -t nat -A prerouting -p tcp -o eth0 -j DNAT --to-destination 1.2.3.4 --random --persistent
nft add rule ip nat prerouting oifname eth0 ip protocol tcp counter dnat 1.2.3.4 random,persistent

Signed-off-by: Shivani Bhardwaj <shivanib134@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>