nfp: improve defines for constants in ethtool

We split rvector stats into two categories - per queue and
stats which are added up into one total counter.  Improve
the defines denoting their number.

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>