IMS mode (Enhanced 4G LTE Mode): replace hard-coded default value with constant.

Change-Id: If06589b4ec5bba2e4bef8dad2db7136ac013f80f
diff --git a/src/com/android/phone/MobileNetworkSettings.java b/src/com/android/phone/MobileNetworkSettings.java
index 637b429..29c7f8a 100644
--- a/src/com/android/phone/MobileNetworkSettings.java
+++ b/src/com/android/phone/MobileNetworkSettings.java
@@ -203,7 +203,7 @@
         SharedPreferences imsPref =
             getSharedPreferences(ImsManager.IMS_SHARED_PREFERENCES, Context.MODE_WORLD_READABLE);
 
-        return imsPref.getBoolean(ImsManager.KEY_IMS_ON, true);
+        return imsPref.getBoolean(ImsManager.KEY_IMS_ON, ImsManager.IMS_DEFAULT_SETTING);
     }
 
     private void setIMS(boolean turnOn) {