!292 修改 recvfrom 参数编译警告

Merge pull request !292 from liuduanfei/gitee_master

components/net/lwip_dhcpd/dhcp_server.c

@@ -306,7 +306,7 @@ static void dhcpd_thread_entry(void *parameter)
     while (1)
     {
         bytes_read = recvfrom(sock, recv_data, BUFSZ - 1, 0,
-                              (struct sockaddr *)&client_addr, &addr_len);
+                              (struct sockaddr *)&client_addr, (socklen_t*)&addr_len);
         if (bytes_read <= 0)
         {
             closesocket(sock);