Add DSCP configuration support for server transport role
Introduce VTY command to configure the Differentiated Services Code Point (DSCP) values for transport "role" server.
The configured DSCP value is applied to the listener socket. Incoming socket connections will then automatically inherit these DSCP settings from the listener socket.
It is not (yet) possible to configure DSCP values for individual active server connections. The setting applies globally via the listener. A later patch will allow DSCP configuration of each individual ASP.
