mISDN: Hardware acceleration is now possible in conjunction with audio recording

Audio recording requires software audio processing.
Both hardware and software processing is simultaniously possible now.

Signed-off-by: Andreas Eversberg <andreas@eversberg.eu>
Signed-off-by: Karsten Keil <keil@b1-systems.de>
Signed-off-by: David S. Miller <davem@davemloft.net>