Don't blindly teardown unvalidated networks when releasing NetworkRequests.

These networks may be on their way to becoming validated at which point
they could satisfy the default NetworkRequest.  This change unifies the
is-this-network-needed code into a single function.

bug:18652378
Change-Id: Ia511d5c66be79b47dd7c9348ec02784ab30b960c
1 file changed