[PATCH v10] eal: RTE_PTR_ADD/SUB char* for compiler optimizations

[Scott Mitchell]

> I will submit a draft for v11 that implements option 3.2. If people
> like this approach we can discuss if/how breaking into multiple
> patches makes sense.

Compilers assume memory is aligned when casting to a specific type
which isn't guaranteed when using these APIs. Returning void* prevents
compilers from making these optimizations and is a safer choice. I
will submit a v12 with APIs returning void* (I think I can still
preserve qualifiers).