Add pci.3 to pve-q35.cfg required by virtio-scsi-single
(commit message reworked from original[1])
As a temporary workaround add always a pci.3 bridge so that if
virtio-scsi-single is used, either directly or indirectly if SCSI and
iothread is selected, the respective bridge is available:
> The case where we do miss the pci.3 bridge is when using
> virtio-scsi-single, regardless of whether io threads are enabled,
> because we always put those controllers on pci bus 3 (see
> QemuServer/PCI.pm)
-- [2]
A long term solution would be to always add those bridges dynamically
and just filter out the ones which are already inside the pve-q35.cfg
file .