core#21992
> Remove -feefilter option
>
> Feefilter option is debug only and it isn't used in any tests, it's wasteful
> to check this option for every peer on every iteration of the message handler
> loop. refs core#21545
> Factor feefilter logic out
>
> Break SendMessages() function into smaller units to improve readability.
> Adds lock assert, as `round()` isn't thread safe.
> closes #21545
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core#24427
> refactor: Release cs_main before MaybeSendFeefilter
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This is a backport of core#21992 and core#24427
Depends on D12182