Fix banning when local node doesn't have the vvec (#2739)

When ProcessMessageBatchedSigShares returns false, it's interpreted as
if an invalid/malicious message was received, causing a ban. So, we should
return "!ban" instead of just "ban".

src/llmq/quorums_signing_shares.cpp

@@ -411,7 +411,7 @@ bool CSigSharesManager::ProcessMessageBatchedSigShares(CNode* pfrom, const CBatc
 
     bool ban = false;
     if (!PreVerifyBatchedSigShares(pfrom->id, sessionInfo, batchedSigShares, ban)) {
-        return ban;
+        return !ban;
     }
 
     std::vector<CSigShare> sigShares;