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: I381d8d446d0754670fb317d8c8ffa0bf85530828
diff --git a/src/com/android/phone/PhoneInterfaceManager.java b/src/com/android/phone/PhoneInterfaceManager.java
index 9a03acc..ea57d02 100755
--- a/src/com/android/phone/PhoneInterfaceManager.java
+++ b/src/com/android/phone/PhoneInterfaceManager.java
@@ -11244,4 +11244,10 @@
             Binder.restoreCallingIdentity(identity);
         }
     }
+
+    @Override
+    public boolean isUsingNewDataStack() {
+        TelephonyPermissions.enforceShellOnly(Binder.getCallingUid(), "isUsingNewDataStack");
+        return getDefaultPhone().isUsingNewDataStack();
+    }
 }