Explain that:
- The method does not cause an actual data stall.
- The detectionMethod parameter refers to
ConnectivityDiagnosticsManager.DataStallReport constants (which
already use an IntDef).
- timestampMillis is relative to SystemClock.elapsedRealtime.
Fixes: 183972768
Test: m
Change-Id: I2eeb79e0e8ec6e8fd3b8fe1dcb1abbf2e6338983
5738b86274