extensions: libxt_MARK: Add translation to nft

extensions: libxt_MARK: Add translation to nft

Add translation for the MARK target to nftables.

Examples:

$ sudo iptables-translate -t mangle -A OUTPUT -j MARK --set-mark 64
nft add rule ip mangle OUTPUT counter meta mark set 0x40

$ sudo iptables-translate -t mangle -A OUTPUT -j MARK --set-xmark 0x40/0x32
nft add rule ip mangle OUTPUT counter meta mark set mark xor 0x40 and 0x32

$ sudo iptables-translate -t mangle -A OUTPUT -j MARK --or-mark 64
nft add rule ip mangle OUTPUT counter meta mark set mark or 0x40

$ sudo iptables-translate -t mangle -A OUTPUT -j MARK --and-mark 64
nft add rule ip mangle OUTPUT counter meta mark set mark and 0x40

$ sudo iptables-translate -t mangle -A OUTPUT -j MARK --xor-mark 64
nft add rule ip mangle OUTPUT counter meta mark set mark xor 0x40

Signed-off-by: Roberto García <rodanber@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>