'''Summary:''' Make sure the file opened (for fd or mapping) at restore is "the same" as it was on dump
CRIU doesn't carry files contents (except for ghost ones) into images. Thus on dump it saves some "meta" for file to validate it's "the same" on restore. Currently this meta includes only the file size. The task is to add some cookie value that's somehow affected by file's contents. This is primarily needed to reduce the possibility to restore with wrong libraries.