Set app_idle_constants in NetPolicyTestsPreparer is not always successful(suspect timing issue).
Set app_idle_constants in AbstractRestrictBackgroundNetworkTestCase again to make sure.
Bug: 115393390
Test: atest com.android.cts.net.HostsideRestrictBackgroundNetworkTests#testAppIdleMetered_whenCharging
Change-Id: I41148bc7eea0825537133f0471ceefeb5b05d763