CVE-2025-21726: padata: avoid UAF for reorder_work

JIRA: https://issues.redhat.com/browse/RHEL-81522
CVE: CVE-2025-21726
MR: !6499 (merged)

This MR backports the 3-patch series that includes the fix to CVE-2025-21726 as well as two other minor cleanup and fix patches.

Signed-off-by: Waiman Long longman@redhat.com