5 lwip sock udp设置超时时间后，阻塞

#define RT_LWIP_UDP
#define RT_LWIP_TCP
#define RT_LWIP_RAW
#define RT_MEMP_NUM_NETCONN 12
#define RT_LWIP_PBUF_NUM 16
#define RT_LWIP_RAW_PCB_NUM 4
#define RT_LWIP_UDP_PCB_NUM 12
#define RT_LWIP_TCP_PCB_NUM 4
#define RT_LWIP_TCP_SEG_NUM 40
#define RT_LWIP_TCP_SND_BUF 8196
#define RT_LWIP_TCP_WND 8196
#define RT_LWIP_TCPTHREAD_PRIORITY 10
#define RT_LWIP_TCPTHREAD_MBOX_SIZE 8
#define RT_LWIP_TCPTHREAD_STACKSIZE 1024
#define RT_LWIP_ETHTHREAD_PRIORITY 12
#define RT_LWIP_ETHTHREAD_STACKSIZE 1024
#define RT_LWIP_ETHTHREAD_MBOX_SIZE 8
#define LWIP_NETIF_STATUS_CALLBACK 1
#define LWIP_NETIF_LINK_CALLBACK 1
#define SO_REUSE 1
#define LWIP_SO_RCVTIMEO 1
#define LWIP_SO_SNDTIMEO 1
#define LWIP_SO_RCVBUF 1
#define LWIP_SO_LINGER 0
#define LWIP_NETIF_LOOPBACK 0
#define RT_LWIP_USING_PING