net/traefik: Update to upstream release 2.6.1

Details:

• Bugfix release, see https://github.com/traefik/traefik/releases/tag/v2.6.1
• No breaking changes, see https://doc.traefik.io/traefik/migration/v2/#v260-to-v261

MFH: 2022Q1
(cherry picked from commit 0789ad8bff08a8644c7e66113a90f32ee723c9c5)