First cut of management control protocol.

First cut of management control protocol.

Defines a management control protocol between the switch and NOX.
Currently, this is only used by vswitchd.  It allows the configuration
and monitoring of a switch as a whole, as opposed to the flow table view
provided by OpenFlow.  To enable, add the appropriate "mgmt" keys to
"vswitchd.conf".  Better docs will be forthcoming...