Fix the memory leak in TetherSettings

https://code.google.com/p/android/issues/detail?id=210848

We need to close the bluetooth adapter's profile proxy in OnDestroy 
method, or it will cause TetherSettings object to be held and won't
release. And finally it will cause OOM issue.
Change-Id: Id7667f751697c8ef9fccaaabfed28a91d4fa4960
Signed-off-by: 宋凯伦 <songkailun@xiaomi.com>

src/com/android/settings/TetherSettings.java

@@ -182,6 +182,16 @@ public class TetherSettings extends SettingsPreferenceFragment
                 com.android.internal.R.array.config_mobile_hotspot_provision_app);
     }
 
+    @Override
+    public void onDestroy() {
+        BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
+        BluetoothProfile profile = mBluetoothPan.getAndSet(null);
+        if (profile != null && adapter != null) {
+            adapter.closeProfileProxy(BluetoothProfile.PAN, profile);
+        }
+        super.onDestroy();
+    }
+
     @Override
     public void onSaveInstanceState(Bundle savedInstanceState) {
         savedInstanceState.putInt(TETHER_CHOICE, mTetherChoice);