fix: set TCP transport every time when setting the config

Author: huming2207

include/mqtt_client.h

@@ -336,7 +336,7 @@ typedef struct esp_mqtt_client_config_t {
         int refresh_connection_after_ms; /*!< Refresh connection after this value (in milliseconds) */
         bool disable_auto_reconnect;     /*!< Client will reconnect to server (when errors/disconnect). Set
                                  `disable_auto_reconnect=true` to disable */
-        esp_transport_handle_t transport; /*!< Custom transport handle to use. Warning: The transport should be valid during the client lifetime and is destroyed when esp_mqtt_client_destroy is called. */
+        esp_transport_handle_t transport; /*!< Custom transport handle to use, leave it NULL to allow MQTT client create or recreate its own. Warning: The transport should be valid during the client lifetime and is destroyed when esp_mqtt_client_destroy is called. */
         struct ifreq * if_name; /*!< The name of interface for data to go through. Use the default interface without setting */
     } network; /*!< Network configuration */
     /**

mqtt_client.c

@@ -526,9 +526,8 @@ esp_err_t esp_mqtt_set_config(esp_mqtt_client_handle_t client, const esp_mqtt_cl
     } else {
         client->config->reconnect_timeout_ms = MQTT_RECON_DEFAULT_MS;
     }
-    if (config->network.transport) {
-        client->config->transport = config->network.transport;
-    }
+    
+    client->config->transport = config->network.transport;
 
     if (config->network.if_name) {
         client->config->if_name = calloc(1, sizeof(struct ifreq) + 1);