Obtain BluetoothAdapter through BluetoothManager

BluetoothAdapter.getDefaultAdapter is deprecated and should be replaced
with BluetoothManager.

The AttributionSource is not necessarily set properly with
BluetoothAdapter.getDefaultAdapter, and may depend on which package is
returned first by PackageManager.getPackagesForUid. This has been
causing some flaky failures in presubmit.

Fixes: 332225348
Test: atest
Change-Id: I2f066f1a90a3c6fed7885f4bbee870abf96f664d

Tethering/src/com/android/networkstack/tethering/TetheringDependencies.java

@@ -156,6 +156,7 @@ public abstract class TetheringDependencies {
     /**
      * Get a reference to BluetoothAdapter to be used by tethering.
      */
+    @Nullable
     public abstract BluetoothAdapter getBluetoothAdapter();
 
     /**

Tethering/src/com/android/networkstack/tethering/TetheringService.java

@@ -30,6 +30,7 @@ import static android.net.dhcp.IDhcpServer.STATUS_UNKNOWN_ERROR;
 
 import android.app.Service;
 import android.bluetooth.BluetoothAdapter;
+import android.bluetooth.BluetoothManager;
 import android.content.Context;
 import android.content.Intent;
 import android.net.IIntResultListener;
@@ -377,7 +378,11 @@ public class TetheringService extends Service {
 
             @Override
             public BluetoothAdapter getBluetoothAdapter() {
-                return BluetoothAdapter.getDefaultAdapter();
+                final BluetoothManager btManager = getSystemService(BluetoothManager.class);
+                if (btManager == null) {
+                    return null;
+                }
+                return btManager.getAdapter();
             }
         };
     }