Revert "net: Avoid duplicate getheaders requests." PR #8054

This reverts commit f93c2a1b7e.

This can cause synchronization to get stuck.

src/main.cpp

@@ -5835,13 +5835,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
-        // If we already know the last header in the message, then it contains
-        // no new information for us.  In this case, we do not request
-        // more headers later.  This prevents multiple chains of redundant
-        // getheader requests from running in parallel if triggered by incoming
-        // blocks while the node is still in initial headers sync.
-        const bool hasNewHeaders = (mapBlockIndex.count(headers.back().GetHash()) == 0);
-
         CBlockIndex *pindexLast = NULL;
         BOOST_FOREACH(const CBlockHeader& header, headers) {
             CValidationState state;
@@ -5862,7 +5855,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         assert(pindexLast);
         UpdateBlockAvailability(pfrom->GetId(), pindexLast->GetBlockHash());
 
-        if (nCount == MAX_HEADERS_RESULTS && hasNewHeaders) {
+        if (nCount == MAX_HEADERS_RESULTS) {
             // Headers message had its maximum size; the peer may have more headers.
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
             // from there instead.