af_iucv: handle non-accepted sockets after resuming from suspend

After resuming from suspend, all af_iucv sockets are disconnected.
Ensure that iucv_accept_dequeue() can handle disconnected sockets
which are not yet accepted.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>