extensions: libipt_ah: Add translation to nft

extensions: libipt_ah: Add translation to nft

Add translation for Authentication Header to nftables.

Examples:

$ sudo iptables-translate -A INPUT -p 51 -m ah --ahspi 500 -j DROP
nft add rule ip filter INPUT ah spi 500 counter drop

$ sudo iptables-translate -A INPUT -p 51 -m ah --ahspi 500:600 -j DROP
nft add rule ip filter INPUT ah spi 500-600 counter drop

$ sudo iptables-translate -A INPUT -p 51 -m ah ! --ahspi 50 -j DROP
nft add rule ip filter INPUT ah spi != 50 counter drop

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