can: esd_usb2: Fix can_dlc value for received RTR, frames

BugLink: http://bugs.launchpad.net/bugs/1729107

commit 72d92e86 upstream.

The dlc member of the struct rx_msg contains also the ESD_RTR flag to
mark received RTR frames. Without the fix the can_dlc value for received
RTR frames would always be set to 8 by get_can_dlc() instead of the
received value.

Fixes: 96d8e903 ("can: Add driver for esd CAN-USB/2 device")
Signed-off-by: Stefan Mätje <stefan.maetje@esd.eu>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/can/usb/esd_usb2.c

@@ -333,7 +333,7 @@ static void esd_usb2_rx_can_msg(struct esd_usb2_net_priv *priv,
 		}
 
 		cf->can_id = id & ESD_IDMASK;
-		cf->can_dlc = get_can_dlc(msg->msg.rx.dlc);
+		cf->can_dlc = get_can_dlc(msg->msg.rx.dlc & ~ESD_RTR);
 
 		if (id & ESD_EXTID)
 			cf->can_id |= CAN_EFF_FLAG;