- Restore nftables as default backend (bsc#1102761). nftables and
iptables can co-exist but the 'nat' table had a bug which was fixed
in kernel-4.18.

- Update to 0.6.1. Some of the changes are:
* Correct source/destination in rich rule masquerade
* Only modify ifcfg files for permanent configuration changes
* Fix a backtrace when calling common_reverse_rule()
* man firewalld.conf: Show nftables is the default FirewallBackend
* firewall-config: fix some untranslated strings that caused a UI
bug causing rich rules to not be modify-able (bsc#1096542)
* fw_direct: avoid log for untracked passthrough queries
* fixed many issues if iptables is actually iptables-nft
* Use preferred location for AppData files
* ipXtables: fix ICMP block inversion with set-log-denied
* fixes ICMP block inversion with set-log-denied with
IndividualCalls=yes
* nftables: fix set-log-denied if target is not ACCEPT
* fw_direct: strip _direct chain suffix if using nftables
* NetworkManager integration bugfixes.