test: realtek net config default to none

Changing this to none as result of build failures. Wifi needs own configuration
per an enviroment. By setting this to none, net tests are skipped for Realtek
platform.

tools/test_configs/target_configs.json

@@ -8,7 +8,7 @@
         "test_configurations": ["ETHERNET"]
     },
     "REALTEK_RTL8195AM": {
-        "default_test_configuration": "REALTEK_WIFI",
+        "default_test_configuration": "NONE",
         "test_configurations": ["REALTEK_WIFI"]
     }
 }