update multple thread socket server sample code

Guo Wenxue

2018-11-15 8d13b7c3d12e05ce4620e43901a554d80d5c7b23

 ch3_fork/socket_server.c

@@ -142,7 +142,7 @@
         rv=write(clifd, MSG_STR, strlen(MSG_STR));
                if(rv < 0)
                {
                   printf("Write to client by sockfd[%d] failure: %s\n", sockfd, strerror(errno));
                   printf("Write to client by sockfd[%d] failure: %s\n", clifd, strerror(errno));
                   close(clifd);
            exit(0);
                }