extensions: libxt_connmark: Add translation to nft

extensions: libxt_connmark: Add translation to nft

Add translation for connmark to nftables.

Examples:

$ sudo iptables-translate -A INPUT -m connmark --mark 2 -j ACCEPT
nft add rule ip filter INPUT ct mark 0x2 counter accept

$ sudo iptables-translate -A INPUT -m connmark ! --mark 2 -j ACCEPT
nft add rule ip filter INPUT ct mark != 0x2 counter accept

$ sudo iptables-translate -A INPUT -m connmark --mark 10/10 -j ACCEPT
nft add rule ip filter INPUT ct mark and 0xa == 0xa counter accept

$ sudo iptables-translate -A INPUT -m connmark ! --mark 10/10 -j ACCEPT
nft add rule ip filter INPUT ct mark and 0xa != 0xa counter accept

$ sudo iptables-translate -t mangle -A PREROUTING -p tcp --dport 40 -m
connmark --mark 0x40
nft add rule ip mangle PREROUTING tcp dport 40 ct mark 0x40 counter

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