kconfig check: enable NFT_COMPAT for iptables-nft wrapper

we're not in the nftables only world yet, things like docker and tailscale only work with the iptables command. those programs expect iptable-modules, which we make available to nftables over the nftables/iptables compat layer.

fixes various issues, that docker doesn't run on device xy, as bringing up networking fails. e.g.: https://gitlab.com/postmarketOS/pmaports/-/issues/2328