esp_netif, examples: esp_netif_init() moved into ESP_ERROR_CHECK()

esp_netif_init() returns standard esp_err_t error code (unlike tcpip_adapter init), so shall be checked for the return value
Also to make the initialization code more consistent.

examples/provisioning/custom_config/main/app_main.c

@@ -84,7 +84,7 @@ static void start_softap_provisioning(void)
 void app_main(void)
 {
     /* Initialize networking stack */
-    esp_netif_init();
+    ESP_ERROR_CHECK(esp_netif_init());
 
     /* Create default event loop needed by the
      * main app and the provisioning service */