implement Thread Border Router e2e integration test

This implements a basic border routing test case (ping) and demonstrates a
valid test environment for Thread Border Router test cases.

Later we can add more packet verifications and more test cases.

Bug: 295843010
Test: atest android.net.ThreadBorderRouterTest

Change-Id: Ifb9b6d45539143a227c2bc0ed69b5c3167ef9acd
diff --git a/thread/TEST_MAPPING b/thread/TEST_MAPPING
index ec1cc08..d3765f1 100644
--- a/thread/TEST_MAPPING
+++ b/thread/TEST_MAPPING
@@ -8,5 +8,10 @@
     {
       "name": "ThreadNetworkUnitTests"
     }
+  ],
+  "postsubmit": [
+    {
+      "name": "ThreadNetworkIntegrationTests"
+    }
   ]
 }