删除多连接内容，只支持单连接

Drivers/BSP/NET/net_select.c

@@ -209,8 +209,7 @@ int net_poll_events(net_pollfd *fds, int nfds, int timeout) {
             }
 
             /* 检查挂起（连接断开） */
-            if ((NET_SOCK_STATE_TCP_ACCEPT == p_sock->state) ||
-                (NET_SOCK_STATE_CLOSED == p_sock->state)) {
+            if (NET_SOCK_STATE_CLOSED == p_sock->state) {
                 fds[i].revents |= NET_POLLHUP;
                 ready++;
             }