[PATCH] drivers/isdn/: add missing #includes

Every file should #include the headers containing the prototypes for its
global functions.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Armin Schindler <armin@melware.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>