isdn: fix multiple sleep_on races

The isdn core code uses a couple of wait queues with
interruptible_sleep_on, which is racy and about to get
removed from the kernel. Fortunately, we know for each case
what we are waiting for, so they can all be converted to
the better wait_event_interruptible interface.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>