net/ena: refactor getting IO queues capabilities

net/ena: refactor getting IO queues capabilities

Reading values from the device is about the maximum capabilities of the
device. Because of that, the names of the fields storing those values,
functions and temporary variables, should be more descriptive in order
to improve self documentation of the code.

In connection with this, the way of getting maximum queue size could be
simplified - no hardcoded values are needed, as the device is going to
send it's capabilities anyway.

Signed-off-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Igor Chauskin <igorch@amazon.com>
Reviewed-by: Guy Tzalik <gtzalik@amazon.com>