Merge #16188: net: Document what happens to getdata of unknown type

dddd927 net: Document what happens to getdata of unknonw type (MarcoFalke)

Pull request description:

  Any getdata of unknown type will never be processed and blocks all future messages from a peer. This isn't obviously clear from reading the code, so document it.

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Tree-SHA512: 4f8e43bbe6534242facfcfffae28b7a6aa2d228841fa2146a87d494e69f614b0da23cf7a5f3d4367358a7c1981fe2ec196a21c437ae1653f1c7e0351be22598a

Author: fanquake

src/net_processing.cpp

@@ -1555,6 +1555,11 @@ 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()) {
@@ -3260,6 +3265,7 @@ 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;