enhance: when setting the log output file, stellar still outputs necessary log information to stderr

src/packet_io/dumpfile_io.cpp

@@ -205,7 +205,7 @@ static void *dumpfile_thread(void *arg)
             ATOMIC_SET(&handle->io_thread_wait_exit, 1);
         }
 
-        PACKET_IO_LOG_STATE("dumpfile io thread waiting exit");
+        PACKET_IO_LOG_STATE("dumpfile io thread has processed all pcap files, wait for exit");
         sleep(1);
     }