Extension "uplink-status-propagation" does not allow to modify existing
ports. This extension only enables the creation of new ports with
this new flag.
Similar to [1], this patch changes the default behaviour of the
exiting ports: if no "propagate_uplink_status" flag is present, "True"
is returned now. The aim of this change is to enable this feature for
all existing ports, that is usually the aim of an administrator when
enables this extension.
[1]https://bugs.launchpad.net/neutron/+bug/1888487
Closes-Bug: #1967881
Related-Bug: #1888487
Change-Id: Ica5b76e0a9a5ae12f764c66be259d7f3cd5b248b