util: increase filechunkiter size to 128k util.filechunkiter has been using a chunk size of 64k for more than 10 years, also in years where Moore's law still was a law. It is probably ok to bump it now and perhaps get a slight win in some cases. Also, largefiles have been using 128k for a long time. Specifying that size multiple times (or forgetting to do it) seems a bit stupid. Decreasing it to 64k also seems unfortunate. Thus, we will set the default chunksize to 128k and use the default everywhere.