Make wallpaper_file a mlstrustedobject to permit writes from any app level.

file.te

@@ -54,7 +54,7 @@ type cache_file, file_type, mlstrustedobject;
 # Default type for anything under /efs
 type efs_file, file_type;
 # Type for wallpaper file.
-type wallpaper_file, file_type;
+type wallpaper_file, file_type, mlstrustedobject;
 
 # All devices have bluetooth efs files. But they
 # vary per device, so this type is used in per

system.te

@@ -148,7 +148,7 @@ allow system apk_data_file:file { relabelfrom relabelto };
 # Relabel wallpaper.
 allow system system_data_file:file relabelfrom;
 allow system wallpaper_file:file relabelto;
-allow system wallpaper_file:file r_file_perms;
+allow system wallpaper_file:file rw_file_perms;
 
 # Property Service write
 allow system system_prop:property_service set;