can: mcp251xfd: mcp251xfd_hw_rx_obj_to_skb(): don't copy data for RTR CAN frames in RX-path

In Classical CAN there are RTR frames. RTR frames have the RTR bit set, may
have a dlc != 0, but contain no data.

This patch changes the RX-path to no copy any data for RTR frames, so that the
data field in the CAN frame stays 0x0.

Link: https://lore.kernel.org/r/20210114153448.1506901-4-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -1474,6 +1474,7 @@ mcp251xfd_hw_rx_obj_to_skb(const struct mcp251xfd_priv *priv,
 						 hw_rx_obj->flags));
 	}
 
+	if (!(hw_rx_obj->flags & MCP251XFD_OBJ_FLAGS_RTR))
 		memcpy(cfd->data, hw_rx_obj->data, cfd->len);
 }