Allow connectivity namespace to enable native level access flags.

Follow the steps: go/android-native-flag-api-manual

Bug: 179099277
Test: m -j
Test: manually verify connection to wifi after flash
Change-Id: Ieb5355d40aec9ed7a42b7ae5b250b696fcf00810
diff --git a/private/network_stack.te b/private/network_stack.te
index ab5a56e..f130e80 100644
--- a/private/network_stack.te
+++ b/private/network_stack.te
@@ -44,3 +44,6 @@
 # in order to invoke side effect of close() on such a socket calling synchronize_rcu()
 # TODO: Remove this permission when 4.9 kernel is deprecated.
 allow network_stack self:key_socket create;
+
+# Grant read permission of connectivity namespace system property prefix.
+get_prop(network_stack, device_config_connectivity_prop)