add support for vfio / sriov

For the purpose of increasing network throughput between host nic and VM, we are planning on adding vfio/sriov support.

Forum discussion is here: https://forum.mergetb.net/t/bringing-sr-iov-device-virtualization-to-merge/111

For XIR it means we need to be able to specify the number of VFs available on each PF/Port and turn them into VF NICModel in a VM.