Bug#909574: firewalld: FirewallBackend=nftables breaks NAT networks in libvirt

[Ralf Jung]

Hi,

According to https://bugzilla.redhat.com/show_bug.cgi?id=1638342, Fedora changed
the default for FirewallBackend back until libvirt works with
FirewallBackend=nftables.  Might be worth doing that in Debian as well?

Kind regards,
Ralf