Using both txid and wtxid-based relay with peers means that we could sometimes
download the same transaction twice, if announced via two different hashes from
different peers.
Use a heuristic of delaying txid-peer-getdata requests by 2 seconds, if we have
at least one wtxid-based peer.
We should eventually request a transaction from all peers that announce
it (assuming we never receive it).
We should prefer requesting from outbound peers over inbound peers.
Enforce the max tx requests in flight, and the eventual expiry of those
requests.
Test author: Suhas Daftuar <sdaftuar@gmail.com>
Adjusted by: MarcoFalke
Fabian Jahr