8387273: Enhance httpserver logging to log when maxConnections is reached

Reviewed-by: jpai, dfuchs, vyazici

src/jdk.httpserver/share/classes/sun/net/httpserver/ServerImpl.java

@@ -538,6 +538,8 @@ class ServerImpl {
                                 if (MAX_CONNECTIONS > 0 && allConnections.size() >= MAX_CONNECTIONS) {
                                     // we've hit max limit of current open connections, so we go
                                     // ahead and close this connection without processing it
+                                    logger.log(Level.DEBUG, "connection limit reached, " +
+                                            "closing accepted connection " + chan);
                                     try {
                                         chan.close();
                                     } catch (IOException ignore) {