net/ena: rework RSS configuration

net/ena: rework RSS configuration

Allow user to specify his own hash key and hash ctrl if the
device is supporting that. HW interprets the key in reverse byte order,
so the PMD reorders the key before passing it to the ena_com layer.

Default key is being set in random matter each time the device is being
initialized.

Moreover, make minor adjustments for reta size setting in terms
of returning error values.

RSS code was moved to ena_rss.c file to improve readability.

Signed-off-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Shai Brandes <shaibran@amazon.com>
Reviewed-by: Shay Agroskin <shayagr@amazon.com>
Reviewed-by: Amit Bernstein <amitbern@amazon.com>