fix: avoid re-propogating old qfcommit messages (#5145)

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## Issue being fixed or feature implemented
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<!--- If it fixes an open issue, please link to the issue here. -->
This fixes an issue where qfcommit messages can be replayed from the
past, then are validated and propagated to other nodes. This patch
changes it so that old qfcommits are not relayed.

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Deployed to a node, and ensured that the log messages are shown.

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src/llmq/blockprocessor.cpp

@@ -91,6 +91,19 @@ void CQuorumBlockProcessor::ProcessMessage(CNode* pfrom, const std::string& msg_
             Misbehaving(pfrom->GetId(), 100);
             return;
         }
+        if (pQuorumBaseBlockIndex->nHeight < (::ChainActive().Height() - GetLLMQParams(type).dkgInterval)) {
+            LogPrint(BCLog::LLMQ, "CQuorumBlockProcessor::%s -- block %s is too old, peer=%d\n", __func__,
+                     qc.quorumHash.ToString(), pfrom->GetId());
+            // TODO: enable punishment in some future version when all/most nodes are running with this fix
+            // Misbehaving(peer.GetId(), 100);
+            return;
+        }
+        if (HasMinedCommitment(type, qc.quorumHash)) {
+            LogPrint(BCLog::LLMQ, "CQuorumBlockProcessor::%s -- commitment for quorum hash[%s], type[%d], quorumIndex[%d] is already mined, peer=%d\n",
+                     __func__, qc.quorumHash.ToString(), uint8_t(type), qc.quorumIndex, pfrom->GetId());
+            // NOTE: do not punish here
+            return;
+        }
     }
 
     {