net: renesas: rswitch: Use napi_gro_receive() in RX

This hardware can receive multiple frames so that using
napi_gro_receive() instead of netif_receive_skb() gets good
performance of RX.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>