fix typo in discard_server example
* Usage: discard_server [local_encaps_port] [remote_encaps_port]
*
* Example
- * Server: $ ./daytime_server 11111 22222
+ * Server: $ ./discard_server 11111 22222
* Client: $ ./client 127.0.0.1 9 0 22222 11111
*/
