ravb: Factorise ravb_set_features

RZ/G2L supports HW checksum on RX and TX whereas R-Car supports on RX.
Factorise ravb_set_features to support this feature.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>