Add selinux policies for network stack service

The policies allow the system server to register a network_stack_service
used to communicate with the network stack process.

Test: atest FrameworksNetTests
Bug: b/112869080
Change-Id: Ib9b7d9150fe4afcce03c8b3dbb36b81c67e39366
diff --git a/private/service_contexts b/private/service_contexts
index c90f93b..467a23d 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -118,6 +118,7 @@
 netd                                      u:object_r:netd_service:s0
 netpolicy                                 u:object_r:netpolicy_service:s0
 netstats                                  u:object_r:netstats_service:s0
+network_stack                             u:object_r:network_stack_service:s0
 network_management                        u:object_r:network_management_service:s0
 network_score                             u:object_r:network_score_service:s0
 network_time_update_service               u:object_r:network_time_update_service:s0