Only push failed tasks to queue

[hyeonLewis]

Proposed changes

In queue, taskQueue contains tasks that need to be reserved to fetch data from peer. In deliver, it delivers the retrieval data packet from peers to fetchResult

However, currently, deliver pushes all requested headers back to taskQueue, which generates redundant staled tasks. This PR fixes to push only invalidated request to queue.

Reference: https://github.com/ethereum/go-ethereum/blob/master/eth/downloader/queue.go#L940

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Further comments

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[blukat29]

Could you retry after this?

git fetch
git cherry-pick 946bfe6