For upstream review: VOID in abstraction for lib-spdk structure

[Douglas-Farley]

From PR #17:

I suppose using an empty struct definition with a #define could work, but I don't see the point. The reason for this change is because they want the network driver abstracted and undefined. This code should support any network driver or controller... not just SPDK. And adding an empty struct definition doesn't do that. If EDK is anything like SPDK all exported header files must be independently compiled.

Originally posted by @johnmeneghini in #17 (comment)

This Issue is to remind to highlight this as part of our q&a/errata during edk2-staging review.