extensions: libxt_CONNMARK: Add translation to nft

extensions: libxt_CONNMARK: Add translation to nft

Add translation for the CONNMARK target to nftables.

The following options have no available translation:

  --save-mark [--nfmask nfmask] [--ctmask ctmask]
  --restore-mark [--nfmask nfmask] [--ctmask ctmask]

Examples:

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --set-mark 0x16
  nft add rule ip mangle PREROUTING counter ct mark set 0x16

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --set-xmark 0x16/0x12
  nft add rule ip mangle PREROUTING counter ct mark set ct mark xor 0x16 and
  0xffffffed

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --and-mark 0x16
  nft add rule ip mangle PREROUTING counter ct mark set ct mark and 0x16

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --or-mark 0x16
  nft add rule ip mangle PREROUTING counter ct mark set ct mark or 0x16

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --save-mark
  nft add rule ip mangle PREROUTING counter ct mark set mark

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --save-mark \
    --mask 0x12
  nft add rule ip mangle PREROUTING counter ct mark set mark and 0x12

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --restore-mark
  nft add rule ip mangle PREROUTING counter meta mark set ct mark

  # iptables-translate -t mangle -A PREROUTING -j CONNMARK --restore-mark \
    --mask 0x12
  nft add rule ip mangle PREROUTING counter meta mark set ct mark and 0x12

Signed-off-by: Roberto García <rodanber@gmail.com>
Acked-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>