Fix a small issue with the BT Tether callback value.

It was incorrect when disabling bt tethering. Note that this had
no practical effect because there's no callback for disabling, but
the change is good for readability's sake.

Change-Id: Id80de58b24e94ec5a8ee38d94fb3016ae7835e43

services/core/java/com/android/server/connectivity/Tethering.java

@@ -451,7 +451,7 @@ public class Tethering extends BaseNetworkObserver {
                 ((BluetoothPan) proxy).setBluetoothTethering(enable);
                 // TODO: Enabling bluetooth tethering can fail asynchronously here.
                 // We should figure out a way to bubble up that failure instead of sending success.
-                int result = ((BluetoothPan) proxy).isTetheringOn() ?
+                int result = ((BluetoothPan) proxy).isTetheringOn() == enable ?
                         ConnectivityManager.TETHER_ERROR_NO_ERROR :
                         ConnectivityManager.TETHER_ERROR_MASTER_ERROR;
                 sendTetherResult(receiver, result);