[PATCH] ring: update Doxygen comments re RING_F_EXACT_SZ

[Ananyev, Konstantin]

> - Add RING_F_EXACT_SZ description to rte_ring_init and
>   rte_ring_create param comments.
> - Fix ring size comments.
> 
> Signed-off-by: Robert Sanford <rsanford at akamai.com>
> ---

Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>

> 2.7.4