Add comment to VisualVoicemailSmsFilterTest.testUnsupportedPdu()

public class VisualVoicemailSmsFilterTest extends TestCase {

    /**

     * b/29123941 iPhone style notification SMS is neither 3GPP nor 3GPP2, but some plain text

     * message. {@link android.telephony.SmsMessage.createFromPdu()} will fail to parse it and

     * return an invalid object, causing {@link NullPointerException} on any operation if not

     * handled.

     */

    public void testUnsupportedPdu() {

        Context context = Mockito.mock(Context.class);

        TelephonyManager telephonyManager = Mockito.mock(TelephonyManager.class);