Add selinux policy for the new net.464xlat.cellular.enabled prop.

This property is written by an .rc file - see aosp/1553819 - and
read by the connectivity mainline code in the system server.

Test: m
Bug: 182333299
Change-Id: Ibac622f6a31c075b64387aadb201ad6cdd618ebd
diff --git a/private/system_server.te b/private/system_server.te
index 349a0b8..e1f97e9 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -734,6 +734,9 @@
 # Read ro.control_privapp_permissions and ro.cp_system_other_odex
 get_prop(system_server, packagemanager_config_prop)
 
+# Read the net.464xlat.cellular.enabled property (written by init).
+get_prop(system_server, net_464xlat_fromvendor_prop)
+
 # Create a socket for connections from debuggerd.
 allow system_server system_ndebug_socket:sock_file create_file_perms;