Comment 8 for bug 1665698

Let me outline on the /etc/qemu-ifup a bit - or at least my understanding of it.
If you happen to run "type=ethernet" networking the script gets to be important.
See https://libvirt.org/formatdomain.html#elementsNICSEthernet
In general this is not recommended for various security reasons (you have to give libvirt/qemu more permissions/capabilities to get this working).
Now if you have type=ethernet and no script set, then the default is /etc/qemu-ifup, maybe that is how it gets this "config" in your case.

The Openstack commit you referred to could absolutely be related as well.
But it should not be in your software stack in your case right?

If applied this would make the xml instead `script=""` not set anything and yes - in that case it would then fall back to /etc/qemu-ifup which might tickle down to showing your issue.