Do nothing when choosing file transfer when in accessory mode

- Before this CL, the device will be disconnected and reconnected
  to accessory mode when choosing "File transfer/Android Auto" in
  accessory mode. Because the USB menu didn't check state of
  function, it should do nothing when choosing
  "File transfer/Android Auto" in accessory mode.

  This CL add condition to check state of function, it will do
  nothing when choosing "File transfer/Android Auto" in
  accessory mode.

Bug: 162451162
Test: make -j42 RunSettingsRoboTests
Change-Id: I1749c6c43d2a192e4ce1bf1ae5343ff8deafbe48
Merged-In: I1749c6c43d2a192e4ce1bf1ae5343ff8deafbe48
(cherry picked from commit 3251a04ba3)

tests/robotests/src/com/android/settings/connecteddevice/usb/UsbDetailsFunctionsControllerTest.java

@@ -263,6 +263,18 @@ public class UsbDetailsFunctionsControllerTest {
                 UsbManager.FUNCTION_MTP);
     }
 
+    @Test
+    public void onRadioButtonClicked_functionMtp_inAccessoryMode_doNothing() {
+        mRadioButtonPreference.setKey(UsbBackend.usbFunctionsToString(UsbManager.FUNCTION_MTP));
+        doReturn(UsbManager.FUNCTION_ACCESSORY).when(mUsbBackend).getCurrentFunctions();
+
+        mDetailsFunctionsController.mPreviousFunction = UsbManager.FUNCTION_ACCESSORY;
+        mDetailsFunctionsController.onRadioButtonClicked(mRadioButtonPreference);
+
+        assertThat(mDetailsFunctionsController.mPreviousFunction).isEqualTo(
+                UsbManager.FUNCTION_ACCESSORY);
+    }
+
     @Test
     public void onRadioButtonClicked_clickSameButton_doNothing() {
         mRadioButtonPreference.setKey(UsbBackend.usbFunctionsToString(UsbManager.FUNCTION_PTP));