nfp: split software and hardware vNIC statistics

In preparation for reporting vNIC HW stats on representors
split handling of the SW and HW stats in ethtool -S.
Representors don't have SW stats (since vNIC is assigned
to the VM).

Remove the questionable defines which assume nn variable
exists in the scope.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>