tune2fs: update overhead when toggling journal feature

tune2fs: update overhead when toggling journal feature

When adding or removing journal from a filesystem, we also need to add /
remove journal blocks from overhead stored in the superblock.  Otherwise
total number of blocks in the filesystem as reported by statfs(2) need
not match reality and could lead to odd results like negative number of
used blocks reported by df(1).

Fixes: 9046b4dfd0ce ("mke2fs: set overhead in super block")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>