Allow CTS to include TestNetworkStackLib

This allows CTS tests to verify that the network stack is working
properly, for example by using DHCP parsing code.

Bug: 156062304
Test: atest CaptivePortalApiTest
Change-Id: If52c689f414cc0730226306dae7d84a0283ef273
diff --git a/Android.bp b/Android.bp
index efe8ff1..62a4f43 100644
--- a/Android.bp
+++ b/Android.bp
@@ -215,7 +215,10 @@
     defaults: ["NetworkStackAppDefaults", "NetworkStackReleaseApiLevel"],
     static_libs: ["NetworkStackApiStableLib"],
     manifest: "AndroidManifestBase.xml",
-    visibility: ["//frameworks/base/tests/net/integration"],
+    visibility: [
+        "//frameworks/base/tests/net/integration",
+        "//cts/tests/tests/net",
+    ],
 }
 
 cc_library_shared {