nox/rfproxy: Add new OpenFlow interface

This patch adds rfproxy/OFInterface.{cc,hh} to construct OpenFlow
FlowMod structures using the controller's API. Currently this means
interfacing with rfofmsg.

Signed-off-by: Joe Stringer <joestringernz@gmail.com>
---
v2:
- Fixes initialisation of ofp_flow_mods
nox/rfproxy: Add support for RouteMod structure

Signed-off-by: Joe Stringer <joestringernz@gmail.com>
rflib: Introduce TLV, Match, Action Types for Python

New TLV, Match and Action structures can be used to manipulate
the binary values of matches and actions in human readable forms.
rfserver: Add support for RouteMod structure

When RFClient sends a RouteMod, RFServer will replace the DPID/Port and
forward to RFProxy. Behaviour of RouteInfo->FlowMod messages remains
the same.
rfclient: Replaces RouteInfo with RouteMod