hw/net/can/xlnx-versal-canfd: Simplify DLC conversions

hw/net/can/xlnx-versal-canfd: Simplify DLC conversions

Use QEMU's helper functions can_dlc2len() and can_len2dlc() for
translating between the raw DLC value and the SocketCAN length value.
This also has the side effect of correctly handling received CAN FD
frames with a DLC of 0-8, which was broken previously.

Signed-off-by: Doug Brown <doug@schmorgal.com>
Reviewed-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Reviewed-by: Francisco Iglesias <francisco.iglesias@amd.com>
Message-id: 20240827034927.66659-7-doug@schmorgal.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>