ravb: Rename "ravb_set_features_rx_csum" function to "ravb_set_features_rcar"

Rename "ravb_set_features_rx_csum" function to "ravb_set_features_rcar" and
replace the function pointer "set_rx_csum_feature" with "set_feature".

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Suggested-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>