Remember to cancel lingering when a network again satsifies a NetworkRequest.

When WiFi's score drops and then comes back up we would previously linger
WiFi but forget to cancel the linger timeout, so 30s later WiFi would
unexpectedly tear down.  Also, make sure this is only done for created
Networks as "created" is the signal to initialy match Networks and requests.

bug:18169560
Change-Id: Ia69b110f6473371e556c60b950253758e023b7aa