While testing #1759, I found an issue in the rootless dind entrypoint that it was not respecting the configured MTU for dind docker due to a permission issue. This fixes that.
It turned out too hard to debug configuration issues on the rootless dind daemon as it was not writing any logs to stdout/stderr of the container. This fixes that, so that any rootless dind configuration or startup errors are visible in e.g. the kubectl-logs output.