Comment 3 for bug 1881881

Interesting libvirt's behavior is different between attaching 30 new interfaces from the case when the VM is created with that 30 interfaces in the first place.

In the boot case[1] there will be an extra device added to the guest

    <controller type='pci' index='1' model='pci-bridge'>
      <model name='pci-bridge'/>
      <target chassisNr='1'/>
      <alias name='pci.1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </controller>

and this allows booting with more than 30 NICs.

In the attach case[2] there is no pci-bridge device.

[1] https://paste.opendev.org/show/811300/
[2] https://paste.opendev.org/show/811301/