nfp: don't report standard netdev statistics in ethtool

We have been recently called out as a bad example for reporting
standard netdev statistics as part of ethtool.  Fix that :)

Removing standard statistics allows us to simplify the structure
holding definitions since we no longer have to mux different types
of statistics.

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>