[MS69.1] Fix TrafficStats.init crashs for supplemental process

Supplemental apps has limited capabilities and service discovery
is restricted. Hence, calling TrafficStats.init would result in
crash.

This change includes:
1. Print log instead of crashing process when running into
   any unexpected cases.

Test: atest SupplementalProcessManagerTests
Bug: 216062904
Change-Id: I7f827ccc485c997745779053b5936a6cb30e8219

framework-t/src/android/net/TrafficStats.java

@@ -31,6 +31,7 @@ import android.media.MediaPlayer;
 import android.os.Binder;
 import android.os.Build;
 import android.os.RemoteException;
+import android.util.Log;
 
 import com.android.server.NetworkManagementSocketTagger;
 
@@ -212,6 +213,13 @@ public class TrafficStats {
         }
         final NetworkStatsManager statsManager =
                 context.getSystemService(NetworkStatsManager.class);
+        if (statsManager == null) {
+            // TODO: Currently Process.isSupplemental is not working yet, because it depends on
+            //  process to run in a certain UID range, which is not true for now. Change this
+            //  to Log.wtf once Process.isSupplemental is ready.
+            Log.e(TAG, "TrafficStats not initialized, uid=" + Binder.getCallingUid());
+            return;
+        }
         sStatsService = statsManager.getBinder();
     }