Intel does have option ROMS to allow the devices to boot via PXE, iSCSI Boot or FCoE Boot. However as noted before, this is not avaialble via a SR-IOV VF.
While libvirt has a mechansim by which you may be able to roll your own for a VF provided you have access to the option ROM binary.
Intel does not provide the option ROM other than attached to the NICs, nor have we done any kind of testing of what libvirt advertises is possible. While I doubt this was the answer you were looking for, I've confirmed my original thesis that you can have an emulated device attached to your VM for PXE boot, then use the VF once the OS is up and running.
thanx,
Patrick
