UDF disk format supports in principle file sizes up to 1<<64-1. However
the file space (including holes) is described by a linked list of
extents, each of which can have at most 1GB. Thus the creation and
handling of extents gets unusably slow beyond certain point. Limit the
file size to 4TB to avoid locking up the kernel too easily.
Signed-off-by: Jan Kara <jack@suse.cz>