message: Improve NOTFOUND comment
diff: @@ -1455,12 +1455,19 @@ void static ProcessGetData(CNode* pfrom, const CChainParams& chainparams, CConnm
  if (!vNotFound.empty()) {
  // Let the peer know that we didn't find what it asked for, so it doesn't
  - // have to wait around forever. Currently only SPV clients actually care
  - // about this message: it's needed when they are recursively walking the
  - // dependencies of relevant unconfirmed transactions. SPV clients want to
  - // do that because they want to know about (and store and rebroadcast and
  - // risk analyze) the dependencies of transactions relevant to them, without
  - // having to download the entire memory pool.
  + // have to wait around forever.
  + // SPV clients care about this message: it's needed when they are
  + // recursively walking the dependencies of relevant unconfirmed
  + // transactions. SPV clients want to do that because they want to know
  + // about (and store and rebroadcast and risk analyze) the dependencies
  + // of transactions relevant to them, without having to download the
  + // entire memory pool.
  + // Also, other nodes can use these messages to automatically request a
  + // transaction from some other peer that annnounced it, and stop
  + // waiting for us to respond.
  + // In normal operation, we often send NOTFOUND messages for parents of
  + // transactions that we relay; if a peer is missing a parent, they may
  + // assume we have them and request the parents from us.
  connman->PushMessage(pfrom, msgMaker.Make(NetMsgType::NOTFOUND, vNotFound));
  }
  }
  