Improve handling of unconnecting headers

src/main.h

@@ -126,6 +126,9 @@ static const bool DEFAULT_ENABLE_REPLACEMENT = true;
 /** Maximum number of headers to announce when relaying blocks with headers message.*/
 static const unsigned int MAX_BLOCKS_TO_ANNOUNCE = 8;
 
+/** Maximum number of unconnecting headers announcements before DoS score */
+static const int MAX_UNCONNECTING_HEADERS = 10;
+
 struct BlockHasher
 {
     size_t operator()(const uint256& hash) const { return hash.GetCheapHash(); }