net/mlx4_en: Fix off-by-four in ethtool

NUM_ALL_STATS was not updated with the new four entries, instead
NUM_FLOW_STATS was updated, fix it. that caused off-by-four for all
counters below pf_*_*.

Fixes: b42de4d0

 ('net/mlx4_en: Show PF own statistics via ethtool')
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>