Add TEST_MAPPING config for CTS postsubmit

The new configuration runs tests on physical devices with SIM cards.
This is only done in postsubmit, as such tests can only run a few (~2) times a day due to
availability of the devices.

This configuration allows running all tests, so there is no annotation filter.

Change-Id: If95e4deeed8098327023f99e6e610331b8e86a0f
Test: TH validates TEST_MAPPING configurations

tests/cts/net/TEST_MAPPING

@@ -19,5 +19,12 @@
         }
       ]
     }
+  ],
+  // Tests on physical devices with SIM cards: postsubmit only for capacity constraints
+  "mainline-postsubmit": [
+    {
+      "name": "CtsNetTestCasesLatestSdk[CaptivePortalLoginGoogle.apk+NetworkStackGoogle.apk+com.google.android.resolv.apex+com.google.android.tethering.apex]",
+      "keywords": ["sim"]
+    }
   ]
 }