drivers: can: mcan: acknowledge all received frames

The Bosch M_CAN IP does not support RX filtering of the RTR bit, so the
driver handles this bit in software.

If a recevied frame matches a filter with RTR enabled, the RTR bit of
the frame must match that of the filter in order to be passed to the RX
callback function. If the RTR bits do not match the frame must be
dropped.

Improve the readability of the the logic for determining if a frame
should be dropped and add a missing FIFO acknowledge write for dropped
frames.

Fixes: #47204

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>