[AF_IUCV/IUCV]: smp_call_function deadlock

Calling smp_call_function can lead to a deadlock if it is called
from tasklet context. 
Fixing this deadlock requires to move the smp_call_function from the
tasklet context to a work queue. To do that queue the path pending
interrupts to a separate list and move the path cleanup out of
iucv_path_sever to iucv_path_connect and iucv_path_pending.
This creates a new requirement for iucv_path_connect: it may not be
called from tasklet context anymore. 
Also fixed compile problem for CONFIG_HOTPLUG_CPU=n and
another one when walking the cpu_online mask. When doing this, 
we must disable cpu hotplug.

Signed-off-by: Frank Pavlic <fpavlic@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/iucv/iucv.h

@@ -16,7 +16,7 @@
  * completed a register, it can exploit the other functions.
  * For furthur reference on all IUCV functionality, refer to the
  * CP Programming Services book, also available on the web thru
- * www.ibm.com/s390/vm/pubs, manual # SC24-5760
+ * www.vm.ibm.com/pubs, manual # SC24-6084
  *
  * Definition of Return Codes
  * - All positive return codes including zero are reflected back