if NM destroyed your virbr0 connection, you can try to create virbr0 again by yourself typing:
$ virsh
virsh # net-destroy default virsh # net-start default
After executing these commands, there should be newly configured virbr0.
if NM destroyed your virbr0 connection, you can try to create virbr0 again by yourself typing:
$ virsh
virsh # net-destroy default
virsh # net-start default
After executing these commands, there should be newly configured virbr0.