Hi.

Summary

Currently _network_event_cb pass pointer to system_event_t into _network_event_queue, instead of value.
I think this wrong. And this pull request fix that.

Description

Method esp_event_loop_task that calls _network_event_cb stores system_event_t in stack:

static void esp_event_loop_task(void *pvParameters)
{
    while (1) {
        system_event_t evt;
        if (xQueueReceive(s_event_queue, &evt, portMAX_DELAY) == pdPASS) {
            esp_err_t ret = esp_event_process_default(&evt);
            if (ret != ESP_OK) {
                ESP_LOGE(TAG, "default event handler failed!");
            }
            ret = esp_event_post_to_user(&evt);
            if (ret != ESP_OK) {
                ESP_LOGE(TAG, "post event to user fail!");
            }
        }
    }
}

So when _network_event_cb sent pointer in _network_event_queue it stores pointer to stack in queue. And if several events occurs it send the same value of pointer to _network_event_queue. It is not that we want.

And more, when _network_event_task reads this pointer, value of system_event_t may be corrupt, because in this time in parallel task method esp_event_loop_task calls xQueueReceive that replacing system_event_t.