Update ConnectivityService.getSignalStrengthThresholds so that thresholds are created for multilayer requests. Bug: 173650494 Bug: 171991028 Test: atest FrameworksNetTests atest FrameworksNetIntegrationTests atest CtsNetTestCasesLatestSdk Change-Id: Ib3b9f52cf371efd1c7d9b176565c7ea8c46375f1