Do not search for a panic task in s390x dumpfiles that are marked as

a "live dump".  Without the patch, an exhaustive, unnecessary, search
of all kernel stacks that looks for evidence of a system crash may
find an invalid reference in a task's kernel stack due to the common
zero-based user and kernel virtual address space ranges of the s390x,
causing the task to be mistakenly set as the "PANIC" task.
(holzheu@linux.vnet.ibm.com, anderson@redhat.com)

task.c

@@ -6750,6 +6750,9 @@ get_dumpfile_panic_task(void)
         } else if (LKCD_DUMPFILE())
 		return(get_lkcd_panic_task());
 
+	if (pc->flags2 & LIVE_DUMP)
+		return NO_TASK;
+
 	if (get_active_set())
 		return(get_active_set_panic_task());