can: drivers: add len8_dlc support for esd_usb2 CAN adapter

Support the Classical CAN raw DLC functionality to send and receive DLC values
from 9 .. 15 for the Classical CAN capable CAN network driver esd_usb that
supports the esd CAN-USB/2 and CAN-USB/Micro devices:

- esd_usb2

Signed-off-by: Stefan Mätje <stefan.maetje@esd.eu>
Tested-by: Stefan Mätje <stefan.maetje@esd.eu>
Link: https://lore.kernel.org/r/20201116184430.25462-2-stefan.maetje@esd.eu


[mkl: rewrapped some long lines]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>