We are ready to remove traffic controller from netd, so
TrafficController::start() should be called from the system server.
This reverts commit c2984fdca8.
Test: atest FrameworksNetTests FrameworksNetIntegrationTests
CtsNetTestCases:android.net.TrafficStatsTest NetworkUsageStatsTest
CtsHostsideNetworkTests
Change-Id: Ic324ad0c064271977ab35d7f55badee00098e196