grant system_server read permission of server_configurable_flags_data

server_configurable_flags_data_file is used for storing server
configurable flags which have been reset during current booting.
system_server needs to read the data to perform related disaster
recovery actions.
For how the data is read, see SettingsToPropertiesMapper.java.

Test: build succeeds & manual on device
Change-Id: Ifa22aecc13af2c574579299d28433622abbe6b85

private/system_server.te

@@ -540,6 +540,12 @@ allow system_server icon_file:file { rw_file_perms unlink };
 # FingerprintService.java does a restorecon of the directory /data/system/users/[0-9]+/fpdata(/.*)?
 allow system_server system_data_file:dir relabelfrom;
 
+# server_configurable_flags_data_file is used for storing server configurable flags which
+# have been reset during current booting. system_server needs to read the data to perform related
+# disaster recovery actions.
+allow system_server server_configurable_flags_data_file:dir r_dir_perms;
+allow system_server server_configurable_flags_data_file:file r_file_perms;
+
 # Property Service write
 set_prop(system_server, system_prop)
 set_prop(system_server, exported_system_prop)