[Indigo] The architecture of Indigo 2.0

After checking with the source code of Indigo 2.0, OF-DPA (CDP) ,and IVS on GitHub, I just draw a simple architecture diagram to show the idea of hardware abstraction layer (HAL). I think the most important part is that Big Switches uses this HAL concept as hardware agnostic to adopt the different forwarding engine / port management implementation in different hardware or platform.