mlx4: remove unused field high_prios

Remove unnecessary field high_prios from mlx4_steer struct and initialization

Signed-off-by: Eugenia Emantayev <eugenia@mellanox.co.il>
Reviewed-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>