mlx4: remove redundant adding of steering type to gid

mlx4_uc_steer_add/release() should not add MLX4_UC_STEER flag to gid.
It is added in mlx4_unicast_attach/detach().

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>