ieee1394: raw1394: defer feature removal of old isoch interface

Known to be affected:
 - libdc1394: prefers video1394 for now, old-style raw1394 support might
   be dropped eventually
 - OpenH323 PWLib, AVC video input module: uses libraw1394's old API

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>