Add a first NetworkAgent CTS test

This is a basic test that only tests register(), markConnected(),
unregister and onNetworkUnwanted. It provides the backbone for
the tests, a harness to test callbacks on NetworkAgent, and
demonstrates how the instrumentation in
ConnectivityService can be used to test this API.

Test: this
Bug: 139268426
Change-Id: I022c9e237fdaec27338047c171c04e5a96cf89e3
diff --git a/tests/cts/net/AndroidManifest.xml b/tests/cts/net/AndroidManifest.xml
index c2b3bf7..baf914f 100644
--- a/tests/cts/net/AndroidManifest.xml
+++ b/tests/cts/net/AndroidManifest.xml
@@ -35,6 +35,11 @@
     <uses-permission android:name="android.permission.WRITE_SECURE_SETTINGS" />
     <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
 
+    <!-- This test also uses signature permissions through adopting the shell identity.
+         The permissions acquired that way include (probably not exhaustive) :
+             android.permission.MANAGE_TEST_NETWORKS
+    -->
+
     <application android:usesCleartextTraffic="true">
         <uses-library android:name="android.test.runner" />
         <uses-library android:name="org.apache.http.legacy" android:required="false" />