Add CtsHostsideNetworkTests to postsubmit.

In preparation for adding them to presubmit.

Test: TEST_MAPPING-only change
Change-Id: Ief37640ed2f1f249d31eefa0b336707b44483455
diff --git a/TEST_MAPPING b/TEST_MAPPING
index bcf5e8b..94adc5b 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -414,6 +414,15 @@
           "exclude-annotation": "androidx.test.filters.RequiresDevice"
         }
       ]
+    },
+    // TODO: upgrade to presubmit. Postsubmit on virtual devices to monitor flakiness only.
+    {
+      "name": "CtsHostsideNetworkTests[CaptivePortalLoginGoogle.apk+NetworkStackGoogle.apk+com.google.android.resolv.apex+com.google.android.tethering.apex]",
+      "options": [
+        {
+          "exclude-annotation": "androidx.test.filters.RequiresDevice"
+        }
+      ]
     }
   ],
   "imports": [