Merge bitcoin/bitcoin#25404: p2p, doc: Use MAX_BLOCKS_TO_ANNOUNCE consistently

e357c89 p2p, doc: Use MAX_BLOCKS_TO_ANNOUNCE consistently (Martin Zumsande)

Pull request description:

  Block announcements via headers may have up to `MAX_BLOCKS_TO_ANNOUNCE = 8` entries according to the definition of this constant.
  However, there are a few spots saying they should have a size _less than_ `MAX_BLOCKS_TO_ANNOUNCE`. Fix these.
  I don't think that this is critical (this only changes behavior when we get a headers announcement with exactly `MAX_BLOCKS_TO_ANNOUNCE` blocks which we can't connect), but it would be nice to handle this limit consistently.

ACKs for top commit:
  dergoegge:
    utACK e357c89 - This PR makes the usage and docs of `MAX_BLOCKS_TO_ANNOUNCE` consistent with its description.

Tree-SHA512: f3772026ab0f402e3a551127ef6e4a98fa9e7af250715fe317c05988b5b33f2f3e098a00e03960d4d28c8bd2b7a97231f7f99f22f1c152c000b2e27b658cf8f2

Author: fanquake

src/net_processing.cpp

@@ -2212,15 +2212,15 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
         LOCK(cs_main);
         CNodeState *nodestate = State(pfrom.GetId());
 
-        // If this looks like it could be a block announcement (nCount <
+        // If this looks like it could be a block announcement (nCount <=
         // MAX_BLOCKS_TO_ANNOUNCE), use special logic for handling headers that
         // don't connect:
         // - Send a getheaders message in response to try to connect the chain.
         // - The peer can send up to MAX_UNCONNECTING_HEADERS in a row that
         //   don't connect before giving DoS points
         // - Once a headers message is received that is valid and does connect,
         //   nUnconnectingHeaders gets reset back to 0.
-        if (!m_chainman.m_blockman.LookupBlockIndex(headers[0].hashPrevBlock) && nCount < MAX_BLOCKS_TO_ANNOUNCE) {
+        if (!m_chainman.m_blockman.LookupBlockIndex(headers[0].hashPrevBlock) && nCount <= MAX_BLOCKS_TO_ANNOUNCE) {
             nodestate->nUnconnectingHeaders++;
             m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, m_chainman.ActiveChain().GetLocator(m_chainman.m_best_header), uint256()));
             LogPrint(BCLog::NET, "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
@@ -4777,7 +4777,7 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
         // Try sending block announcements via headers
         //
         {
-            // If we have less than MAX_BLOCKS_TO_ANNOUNCE in our
+            // If we have no more than MAX_BLOCKS_TO_ANNOUNCE in our
             // list of block hashes we're relaying, and our peer wants
             // headers announcements, then find the first header
             // not yet known to our peer but would connect, and send.