Fixed that data unthrottling not working

The data unthrottling input from data service
is APN name, not APN type. DcTracker should convert
APN to APN types before sending unthrottling information
to data throttler.

Fix: 182885625
Test: atest DcTrackerTest#testDataUnthrottled
Change-Id: I32ad58bb01671cf4c19923cb3010cb5201c86d14