iavf: Limiting RSS queues to CPUs

Limiting RSS queues number to online CPUs number in order to
avoid issues with creating misconfigured RSS queues.

Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>