going by reports in the forum (e.g. [0]) and semi-official qemu
information[1], we should prefer qemu-xhci over nec-usb-xhci
for compatibility purposes, we guard that behind the machine version,
so that guests with a fixed version don't suddenly have a different usb
controller after a reboot (which could potentially break some hardcoded
guest configs)
0: https://forum.proxmox.com/threads/proxmox-usb-connect-disconnect-loop.117063/
1: https://www.kraxel.org/blog/2018/08/qemu-usb-tips/
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
