auto-t: iwd.py: fix full_scan argument

This was not being properly honored when existing networks were
already populated. This poses an issue for any test which uses
full_scan after setting radio values such as signal strength.

autotests/util/iwd.py

@@ -492,6 +492,7 @@ class Device(IWDDBusAbstract):
            main sorting factor.
         '''
         ordered_networks = []
+        if not full_scan:
             for bus_obj in self._station.GetOrderedNetworks():
                 ordered_network = OrderedNetwork(bus_obj, self._bus, self._namespace)
                 ordered_networks.append(ordered_network)