Add global settings for cell radio state

Provide persistable state for cell radio
to handle airplane mode similar to any
other radio in the system.

Change-Id: I87398fe84de3f6a10b0e1002e9e5bf7e61f9441f
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index ca45e62..c531954 100755
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -9074,6 +9074,12 @@
          */
         public static final String SYSTEM_NAVIGATION_KEYS_ENABLED =
                 "system_navigation_keys_enabled";
+
+        /**
+         * Whether cell is enabled/disabled
+         * @hide
+         */
+        public static final String CELL_ON = "cell_on";
     }
 
     /**