[SCSI] zfcp: Ensure all work is cancelled on adapter dequeue

A scheduled work might still be pending, running while the adapter is
in progress to get dequeued from the system. This can lead to an
invalid pointer dereference (Oops).  Once the adpater is set online
again, ensure the nameserver environment is initialized to the
appropriate values again.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>