Alpine Linux should default to nf_tables backend

Alpine linux commands such as "iptables" currently point to the "legacy" variants.

I inquired about this a year ago but never got an answer.

Alpine Linux should default to the nf_tables variants ie iptables-nft.

It's now expected by things like libvirtd, docker, podman etc that you'll have the nf_tables backend.

Worth noting upstream Netfilter team doesn't support legacy any more. Both Debian, and other major distributions all default to the nf_tables.

@Ikke does currently say that awall depends on the legacy framework, perhaps it should be updated.