nftables support

[Nardol]

On Debian Buster, nftables is the default instead of iptables.
NFTables becomes more used.
Implement it on DDOSDeflate would allow to use it more reliably on Debian Buster for example and for users who now use NFTables.

[tvbird]

+1.
it would be great!

[StudioMaX]

nftables is also the default on RHEL/CentOS 8.