ice: enforce RTNL assumption of queue NAPI manipulation

ice: enforce RTNL assumption of queue NAPI manipulation

Instead of making assumptions in comments move them into code.
Be also more precise, RTNL must be locked only when there is
NAPI, and we have VSIs w/o NAPI that call ice_vsi_clear_napi_queues()
during rmmod.

Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>