Add NetworkStack policies for netd and netlink

Allow netd to send network events to the NetworkStack, and allow the
NetworkStack to interact with netlink_route_socket for neighbor
monitoring.

Test: built, booted, WiFi works, no more violations
Bug: 112869080
Change-Id: If212b2897e37e9d249f81ba8139461bce461528e
diff --git a/private/network_stack.te b/private/network_stack.te
index 9d2f2fb..4b88756 100644
--- a/private/network_stack.te
+++ b/private/network_stack.te
@@ -17,6 +17,9 @@
 # The DhcpClient uses packet_sockets
 allow network_stack self:packet_socket create_socket_perms_no_ioctl;
 
+# Monitor neighbors via netlink.
+allow network_stack self:netlink_route_socket nlmsg_write;
+
 allow network_stack app_api_service:service_manager find;
 allow network_stack netd_service:service_manager find;
 allow network_stack radio_service:service_manager find;