wifi: refactor code to match ethernet's init function structure

components/esp32/include/esp_event.h

@@ -165,6 +165,12 @@ esp_err_t esp_event_process_default(system_event_t *event);
   */
 void esp_event_set_default_eth_handlers();
 
+/**
+  * @brief  Install default event handlers for Wi-Fi interfaces (station and AP)
+  *
+  */
+void esp_event_set_default_wifi_handlers();
+
 #ifdef __cplusplus
 }
 #endif

components/esp32/include/esp_wifi_internal.h

@@ -45,6 +45,12 @@ extern "C" {
  *     Alloc resource for WiFi driver, such as WiFi control structure, RX/TX buffer,
  *     WiFi NVS structure among others.
  *
+ * For the most part, you need not call this function directly. It gets called
+ * from esp_wifi_init().
+ *
+ * This function may be called, if you only need to initialize the Wi-Fi driver
+ * without having to use the network stack on top.
+ *
  * @param  config provide WiFi init configuration
  *
  * @return