mISDN: Make clearing B-channel a common function

Clearing B-channel is needed in every driver, so it makes sense
to have it as common function.

Signed-off-by: Karsten Keil <keil@b1-systems.de>
diff --git a/include/linux/mISDNhw.h b/include/linux/mISDNhw.h
index 7f9831d..4af8414 100644
--- a/include/linux/mISDNhw.h
+++ b/include/linux/mISDNhw.h
@@ -168,6 +168,7 @@
 extern int	mISDN_initdchannel(struct dchannel *, int, void *);
 extern int	mISDN_initbchannel(struct bchannel *, int);
 extern int	mISDN_freedchannel(struct dchannel *);
+extern void	mISDN_clear_bchannel(struct bchannel *);
 extern int	mISDN_freebchannel(struct bchannel *);
 extern void	queue_ch_frame(struct mISDNchannel *, u_int,
 			int, struct sk_buff *);