net/traefik: Update to upstream release 2.8.1

Details:

• Bugfix release, see https://github.com/traefik/traefik/releases/tag/v2.8.1
• No breaking config changes: https://doc.traefik.io/traefik/migration/v2/

MFH: 2022Q3
(cherry picked from commit 0a5432373c54bc9febe67fdb127927e431e41525)