This patch fixes a race and some segfaults which i discovered while testing scsi-generic and unmapping with libiscsi.
The first problem is that in iscsi_aio_cancel iscsi_scsi_task_cancel and iscsi_task_mgmt_abort_task_async got called but iscsi_task_mgmt_abort_task_async already calls iscsi_scsi_task_cancel. The second problem is that scsi_free_scsi_task(acb->task) and acb->task = NULL must be done when io is complete or the whole task cancelation has finished. Right now it is done in between. Sorry no native speaker i hope i was able to explain what the problem is. Otherwise Ronnie is informed and perhaps explain the problem too.
