[update] change default lwip stack to lwip2.0.3

components/net/Kconfig

@@ -114,7 +114,7 @@ config RT_USING_LWIP
     if RT_USING_LWIP
         choice
             prompt "lwIP version"
-            default RT_USING_LWIP212
+            default RT_USING_LWIP203
             help
                 Select the lwIP version