net: ena: Make few cosmetic preparations to support large LLQ

Move ena_calc_io_queue_size() implementation closer to the file's
beginning so that it can be later called from ena_device_init()
function without adding a function declaration.

Also add an empty line at some spots to separate logical blocks in
funcitons.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>