net: Document what happens to getdata of unknonw type

src/net_processing.cpp

@@ -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;