ethdev: hide internal structures

[Tyler Retzlaff]

On Tue, Nov 16, 2021 at 10:32:55AM +0000, Ananyev, Konstantin wrote:
>  
> rte_eth_dev,  rte_eth_dev_data, rte_eth_rxtx_callback are internal
> data structures that were used by public inline ethdev functions. 
> Well behaving app should not access these data structures directly.
> So, for well behaving app there should no changes in the code required.
> That what I meant by 'transparent' above.
> But it is still an ABI change, so yes, the app has to be re-compiled. 

so it appears the application was establishing a private context /
vendor extension between the application and a pmd. the application
was abusing access to the rte_eth_devices[] to get the private context
from the rte_eth_dev.

is there a proper / supported way of providing this functionality
through the public api?

> 
> Konstantin