net/atm/signaling.c: remove WAIT_FOR_DEMON code

WAIT_FOR_DEMON code is directly undefined at the beginning
of signaling.c since initial git version and thus never compiled.
This also removes buggy current->state direct access.

Suggested-by: Chas Williams <chas@cmf.nrl.navy.mil>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: David S. Miller <davem@davemloft.net>