gud: set PATH connector property

[Simon Ser <contact@xxxxxxxxxxx>]

Hi Noralf,

Would it be possible to set the PATH connector property based on the
USB port used by gud?

This would give user-space a persistent identifier for the connector:
if the user plugs in a USB display on a given port, the PATH would be
the same even if the machine rebooted or the displays were plugged in
in a different order.

DP-MST already sets this. User-space can use this property to store
output configuration metadata.

Thanks,

Simon