net: ena: Recalculate TX state variables every device reset

With the ability to modify LLQ entry size, the size of packet's
payload that can be written directly to the device changes.
This patch makes the driver recalculate this information every device
negotiation (also called device reset).

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