Persist dark mode when set

When setting dark mode, the changes dont persist

Test: atest UiModeManagerServiceTest
Change-Id: I6c18cf096510d79cff9c0d6eac830f7b9209166c
diff --git a/data/etc/privapp-permissions-platform.xml b/data/etc/privapp-permissions-platform.xml
index e07edd4..fff250c 100644
--- a/data/etc/privapp-permissions-platform.xml
+++ b/data/etc/privapp-permissions-platform.xml
@@ -259,6 +259,8 @@
     </privapp-permissions>
 
     <privapp-permissions package="com.android.shell">
+        <!-- Needed for test only -->
+        <permission name="android.permission.MODIFY_DAY_NIGHT_MODE"/>
         <permission name="android.permission.ACCESS_LOWPAN_STATE"/>
         <permission name="android.permission.BACKUP"/>
         <permission name="android.permission.BATTERY_STATS"/>