nfp: report FW vNIC stats in interface stats

Report in standard netdev stats drops and errors as well as
RX multicast from the FW vNIC counters.

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>