[PATCH] rust: support DPDK API

[Etelson, Gregory]

>
> Re-implementing test-pmd, l3fwd, etc in Rust is OK but not huge leap.

DPDK examples and applications are part of inner infrastructure.
The patch allows external RUST application as well.


> The real benefit would the ability to support PMD's built in Rust.
> That would be much more invasive
>

It's not sure when and even if vendors decide to work on RUST PMD.
Before that happens, there must be native RUST API with RUST-DPDK library 
functions.

In the meanwhile, RUST application can use existing C API.
Also, having RUST inside DPDK can shape existing API for future conversion.