* eth/downloader: use atomic type

* Update eth/downloader/downloader_test.go
Co-authored-by: Martin Holst Swende <martin@swende.se>

* Update eth/downloader/downloader_test.go
Co-authored-by: Martin Holst Swende <martin@swende.se>

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Co-authored-by: Martin Holst Swende <martin@swende.se>