doc: releases: migration-guide: 3.6: removal of run-time CAN RTR filter

Add a note about the removal of the CAN_FILTER_DATA and CAN_FILTER_RTR
flags from the CAN controller driver API.

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

doc/releases/migration-guide-3.6.rst

@@ -179,6 +179,14 @@ Device Drivers and Device Tree
   controllers implement support for this. Applications can still filter on classic CAN/CAN FD frames
   in their receive callback functions as needed.
 
+* The ``CAN_FILTER_DATA`` and ``CAN_FILTER_RTR`` flags for filtering between Data and Remote
+  Transmission Request (RTR) frames were removed since not all CAN controllers implement support for
+  individual RX filtering based on the RTR bit. Applications can now use
+  :kconfig:option:`CONFIG_CAN_ACCEPT_RTR` to either accept incoming RTR frames matching CAN filters
+  or reject all incoming CAN RTR frames (the default). When :kconfig:option:`CONFIG_CAN_ACCEPT_RTR`
+  is enabled, applications can still filter between Data and RTR frames in their receive callback
+  functions as needed.
+
 * The io-channel cells of the following devicetree bindings were reduced from 2 (``positive`` and
   ``negative``) to the common ``input``, making it possible to use the various ADC DT macros with TI
   LMP90xxx ADC devices: