message: net: Document what happens to getdata of unknonw type
diff: @@ -1540,6 +1540,11 @@ void static ProcessGetData(CNode* pfrom, const CChainParams& chainparams, CConnm
  }
  }
  + // Unknown types in the GetData stay in vRecvGetData and block any future
  + // message from this peer, see vRecvGetData check in ProcessMessages().
  + // Depending on future p2p changes, we might either drop unknown getdata on
  + // the floor or disconnect the peer.
  +
  pfrom->vRecvGetData.erase(pfrom->vRecvGetData.begin(), it);
  if (!vNotFound.empty()) {
  @@ -3219,6 +3224,7 @@ bool PeerLogicValidation::ProcessMessages(CNode* pfrom, std::atomic<bool>& inter
  return false;
  // this maintains the order of responses
  + // and prevents vRecvGetData to grow unbounded
  if (!pfrom->vRecvGetData.empty()) return true;
  if (!pfrom->orphan_work_set.empty()) return true;
  