firewalld-0.6.0

This is a large release with the below updates.

User features:

• nftables backend
  This is the new default for all firewalld's abstractions. The direct interface still supports iptables, ip6tables, and ebtables. It is configurable via FirewallBackend in /etc/firewalld.conf - valid values are; nftables, iptables.
• new services: iSNS, mqtt, slp, distcc, salt-master, wsman, finger, nut, svdrp, subversion, apcupsd, etcd, wbem-http, llmnr, rtsp, cockpit, steam, samba-dc, matrix, plex
• updated translations

Developer features:

• flake8 source code checking
• better debug output (tracebacks)
• various testsuite improvements

New requirements:

• kernel >= 4.18
• nftables >= 4.9.0