migrate to cpp app remove irrelevant parts

main/CMakeLists.txt

@@ -1,2 +1,2 @@
-idf_component_register(SRCS "ethernet_example_main.c"
+idf_component_register(SRCS "watch_main.cpp"
                        INCLUDE_DIRS ".")

main/watch_main.cpp

@@ -31,6 +31,10 @@ static const char *TAG = "Watch";
 static esp_eth_handle_t s_eth_handle = NULL;
 static bool s_ethernet_is_connected = false;
 
+extern "C" { // This switch allows the ROS C-implementation to find this main
+void app_main(void);
+}
+
 /** Event handler for IP_EVENT_ETH_GOT_IP */
 static void got_ip_event_handler(void *arg, esp_event_base_t event_base,
                                  int32_t event_id, void *event_data)