连接状态

连接状态 State
　　ESTABLISHED 有一个确定的连接
　　SYN_SENT 活动socket尝试建立连接
　　SYN_RECV 连接请求已经收到
　　FIN_WAIT1 socket已经关闭，链接已经断开。
　　FIN_WAIT2 socket已经关闭，链接在最后断开。
　　TIME_WAIT The socket is waiting after close to handle packets still in the network.
　　CLOSED The socket is not being used.
　　CLOSE_WAIT The remote end has shut down, waiting for the socket to close.
　　LAST_ACK The remote end has shut down, and the socket is closed. Waiting for acknowledgement.
　　LISTEN The socket is listening for incoming connections.
　　CLOSING Both sockets are shut down but we still donot have all our data sent.
　　UNKNOWN The state of the socket is unknown.