mISDN: Fixed false interruption of audio during bridging change.

Transmitted audio data was interrupted if a bridge was enabled or disabled.
Now transmission seamlessly continues during that action.
Fix in hfcmulti.ko

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