Comment # 7 on bug 1158817 from Krasimir Ivanov

(In reply to Giacomo Comes from comment #2)
> Same problem here.
> The issue is caused by the line
>   softdep bridge post: br_netfilter
> in /etc/modprobe.d/00-system.conf introduced in suse-module-tools-15.1.16
> commenting such line makes kvm network work again.

Thank you very much for this hint!
Commenting this line helped me to get back online my virtual machines.