example: init nvs in iperf example

Need to call nvs_flash_init in iperf example

examples/wifi/iperf/main/main.c

@@ -14,6 +14,7 @@
 #include "esp_wifi.h"
 #include "esp_log.h"
 #include "esp_err.h"
+#include "nvs_flash.h"
 
 #include "esp_console.h"
 #include "esp_vfs_dev.h"
@@ -69,6 +70,13 @@ static void initialize_console()
 
 void app_main(void)
 {
+    esp_err_t ret = nvs_flash_init();
+    if (ret == ESP_ERR_NVS_NO_FREE_PAGES) {
+        ESP_ERROR_CHECK(nvs_flash_erase());
+        ret = nvs_flash_init();
+    }
+    ESP_ERROR_CHECK( ret );
+ 
     initialise_wifi();
     initialize_console();