解决at_socket在极限情况下内存泄漏问题

AT模块在执行AT+CLOSE并返回OK后，在实际关闭前（上报URC前）仍然有
可能接收到数据。所以接收数据时需要判断状态是否为AT_SOCKET_CONNECT。

另，at_recv_notice_cb在拒绝数据包时，没有释放数据包内存，从而导致
内在泄漏。

Author: wenbodong2015

components/net/at/at_socket/at_socket.c

@@ -652,14 +652,20 @@ static void at_recv_notice_cb(struct at_socket *sock, at_socket_evt_t event, con
     RT_ASSERT(event == AT_SOCKET_EVT_RECV);
 
     /* check the socket object status */
-    if (sock->magic != AT_SOCKET_MAGIC)
+    if (sock->magic != AT_SOCKET_MAGIC || sock->state != AT_SOCKET_CONNECT)
     {
+        rt_free((void *)buff);
         return;
     }
 
     /* put receive buffer to receiver packet list */
     rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
-    at_recvpkt_put(&(sock->recvpkt_list), buff, bfsz);
+    if (!at_recvpkt_put(&(sock->recvpkt_list), buff, bfsz))
+    {
+        rt_free((void *)buff);
+        rt_mutex_release(sock->recv_lock);
+        return;
+    }
     rt_mutex_release(sock->recv_lock);
 
     rt_sem_release(sock->recv_notice);