udev: net_id: search parent devices for PCI slot number

udev: net_id: search parent devices for PCI slot number

To generate predictable network device names, the code in
udev-builting-net_id.c tries to match the PCI device address
of the network device to the entries in /sys/bus/pci/slots.
However, sometimes the slot number is not associated the
network controller PCI device itself, but rather with one of
its parents.

This change will try to find a match in /sys/bus/pci/slots for
the parents of the PCI network device, if it doesn't find a
match for the device itself.