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/property.te b/private/property.te
index 88f3ec0..e4cbd7a 100644
--- a/private/property.te
+++ b/private/property.te
@@ -19,6 +19,7 @@
 system_internal_prop(last_boot_reason_prop)
 system_internal_prop(localization_prop)
 system_internal_prop(lower_kptr_restrict_prop)
+system_internal_prop(net_464xlat_fromvendor_prop)
 system_internal_prop(netd_stable_secret_prop)
 system_internal_prop(pm_prop)
 system_internal_prop(rollback_test_prop)