This reverts commit 41f6f17d01 ("return 0
(meaning the file is not seekable, as the docs now explain) instead of
4KB for the files in sysfs under Linux") as it seems to be wrong to
return a value different from what "ls -l" or "stat" return here and the
original problem was solved in a better way in the previous commit.
See #9965.
Closes#17818.
a03ece4880