Send updated NetworkAgent score to NetworkFactories when validated.

Previously the score was not sent out causing other NetworkFactories
to have the lower unvalidated score and to repeatedly try to bring
up a new Network only to have it torn down.
Also, avoid logging an error when tearing down a network with only
listening requests.

bug:17726566
Change-Id: I82ff7c9bd5ec962f62a50ad0042c278622953969