Trunk subports don't have a device ID

[Ivar Lazzaro]

When adding a port to a Trunk, it gets bound to the parent's host and gets the owner type trunk:subport.
However, the parent device_id is not passed to the subport itself. This will make checks like the networking_sfc port pair validation fail as it expects both the port pair ports to belong to the same device [0]
Ofc sfc could check the parent's device ID in case of a subport, but I think it also makes sense for the neutron port to show such ID as part of the binding.

[0] https://github.com/openstack/networking-sfc/blob/stable/queens/networking_sfc/db/sfc_db.py#L484-L496