Add automatic OF listener port assigning to snmpit: OF listener cmd option doesnot need the listener string now; a doEnableOpenflowListener is implemented in snmpit to do the assignment; a getUsedOpenflowListenerPorts is added to stacks modules to help the port assignment; the listener can be from 5000 to 65535. The Openflow string is added to all Of related functions names in snmpit.in and stacks modules