Added command line tool to enable/disable new data stack

Provide the temporary command line tool to check whether new
data stack is enabled or not.

Bug: 196597630
Test: adb shell cmd phone get-data-mode
Change-Id: I9f95e7424e6e74af12a0f6780a58fb5732df7300
Merged-In: I9f95e7424e6e74af12a0f6780a58fb5732df7300

telephony/java/com/android/internal/telephony/ITelephony.aidl

@@ -2556,4 +2556,7 @@ interface ITelephony {
      * for the slot, or {@code null} if none is resolved
      */
     String getCarrierServicePackageNameForLogicalSlot(int logicalSlotIndex);
+
+    /** Check if telephony new data stack is enabled. */
+    boolean isUsingNewDataStack();
 }