The "after iptables" clause in the OpenRC service script's depend()
function causes fail2ban to start after iptables, if iptables is
scheduled to start. Here we add "after nftables" as well: nftables is
the successor to iptables, and fail2ban supports it out-of-the-box.
If nftables is scheduled to start, we want to wait until it's done
before starting fail2ban.