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_contexts b/private/property_contexts
index 35bf7eb..d643021 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -279,6 +279,9 @@
 com.android.sdkext.                  u:object_r:module_sdkextensions_prop:s0
 persist.com.android.sdkext.          u:object_r:module_sdkextensions_prop:s0
 
+# Connectivity module
+net.464xlat.cellular.enabled         u:object_r:net_464xlat_fromvendor_prop:s0 exact bool
+
 # Userspace reboot properties
 sys.userspace_reboot.log.         u:object_r:userspace_reboot_log_prop:s0
 persist.sys.userspace_reboot.log. u:object_r:userspace_reboot_log_prop:s0