fix(vd960DBN): MQTT socket 复用 SocketId_TCP，对标官方 WCHNET MQTT 例程

根因分析：iot_connect_broker 自建 socket 与 WCHNET_CreateTcpMqttSocket
创建的 SocketId_TCP 冲突（重复创建），且自建 socket 的 WCHNET_SocketSend
崩溃。官方 MQTT 例程使用统一的 SocketId/SocketId_TCP 模式。

改动：
- peripheral_main.c: 恢复 WCHNET_CreateTcpMqttSocket() 调用
- iot_connect_broker: 不再创建新 socket，直接复用 SocketId_TCP
- 全链路（SocketSend/HandleSockInt/poll）通过 g_iot_socket=SocketId_TCP 统一

vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c

@@ -32,6 +32,7 @@
 
 
 extern uint8_t g_report_active;    // from tcp_json_srv.c, 0=inactive 1=active
+extern uint8_t SocketId_TCP;        // from net_srv.c, MQTT socket created by WCHNET_CreateTcpMqttSocket
 uint8_t  g_iot_socket = 0xFF;          // MQTT TCP socket ID
 IotMqttState g_iot_state = IOT_STATE_DISCONNECTED;
 uint8_t  g_iot_msg_id = 0;             // MQTT packet identifier
@@ -477,46 +478,9 @@ static void iot_send_heartbeat(void) {
  * 连接管理
  *===========================================================================*/
 
-/* 连接到 MQTT Broker */
+/* 连接到 MQTT Broker — 复用 SocketId_TCP（已由 WCHNET_CreateTcpMqttSocket 创建并连接） */
 static void iot_connect_broker(void) {
-    uint8_t broker_ip[4];
-    SOCK_INF sock_inf;
-    uint8_t ret;
-
-    // 解析 broker 地址
-    if (get_ipstr_to_array((char *)iot_net_info.remote_addr, broker_ip) == 0) {
-        // 是 IP 地址 — get_ipstr_to_array 已将结果写入 broker_ip，无需 memcpy
-        PRINT("IOT: broker IP %d.%d.%d.%d:%d\n",
-              broker_ip[0], broker_ip[1], broker_ip[2], broker_ip[3],
-              iot_net_info.mqtt_port);
-    } else {
-        PRINT("IOT: broker hostname=%s (DNS not implemented yet)\n",
-              iot_net_info.remote_addr);
-        return;
-    }
-
-    memset(&sock_inf, 0, sizeof(SOCK_INF));
-    sock_inf.DesPort = iot_net_info.mqtt_port;
-    sock_inf.SourPort = local_net_cfg.port_dev_udp + 1;  // 参考 WCHNET_CreateTcpMqttSocket
-    sock_inf.ProtoType = PROTO_TYPE_TCP;
-    sock_inf.RecvBufLen = RECE_BUF_LEN;
-    memcpy(sock_inf.IPAddr, broker_ip, 4);
-
-    ret = WCHNET_SocketCreat(&g_iot_socket, &sock_inf);
-    if (ret != WCHNET_ERR_SUCCESS) {
-        PRINT("IOT: SocketCreat failed: 0x%02X\n", ret);
-        g_iot_socket = 0xFF;
-        return;
-    }
-
-    ret = WCHNET_SocketConnect(g_iot_socket);
-    if (ret != WCHNET_ERR_SUCCESS) {
-        PRINT("IOT: SocketConnect failed: 0x%02X\n", ret);
-        WCHNET_SocketClose(g_iot_socket, TCP_CLOSE_NORMAL);
-        g_iot_socket = 0xFF;
-        return;
-    }
-
+    g_iot_socket = SocketId_TCP;  // 复用已创建的 MQTT socket
     g_iot_state = IOT_STATE_TCP_CONNECTING;
     _iot_connect_start = mstick();
     PRINT("IOT: TCP connecting to broker (sock=%d)...\n", g_iot_socket);

vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/peripheral_main.c

@@ -238,9 +238,15 @@ void Main_Circulation(void)
         if(g_net_state.flag == 2)
         {
             if(g_sub_code_enable.iot_enable){
-                // IoT MQTT 模式由 iot_connect_broker() 自行管理 socket，
-                // 不要在此重复创建，直接推进状态
-                g_net_state.flag = 3;
+                if(iot_net_info.mode == IOT_Addr_IP_Mode){
+                    if(get_ipstr_to_array(iot_net_info.remote_addr, RemoteIP) == 0){
+                        WCHNET_CreateTcpMqttSocket();
+                    }
+                }
+                else{
+                    //DNS 
+                }
+                
             }
             else
             {