get_host_firewall() reads `nft -j list ruleset` as root and returns every
chain with its family, table, hook, priority and policy, and every rule as
matches and a verdict. Rules iptables-nft wrote show their extensions in nft's
JSON only as an opaque `xt`, so the tables iptables manages are taken from
iptables-save instead; a legacy iptables is kept beside nft's tables, since
both apply. A condition the parse does not model is an `unknown` match with
its text, never left out. Without root neither tool can be read, and
HostFirewallUnavailable is raised rather than a host without rules.
A driver supplies only _run_host_firewall_command(command, privileged=).
Version 4.21.0.
christianmanivong