When using iPXE as an option ROM for a PCI USB controller (e.g. via
qemu's "-device nec-usb-xhci,romfile=..." syntax), the ROM prefix will
set the PCI bus:dev.fn address of the USB controller as the PCI
autoboot device.  This will cause iPXE to fail to boot from any
detected USB network devices, since they will not match the autoboot
bus type (or location).

Fix by allowing the autoboot bus type and location to match against
the network device or any of its parent devices.  This allows the
match to succeed for USB network devices attached to the selected PCI
USB controller.

Reported-by: Dan Ellis <Dan.Ellis@displaylink.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>