Linux: Work around kernel bugs in chmod on /proc/self/fd paths [BZ #14578]

It appears that the ability to change symbolic link modes through such
paths is unintended.  On several file systems, the operation fails with
EOPNOTSUPP, even though the symbolic link permissions are updated.
The expected behavior is a failure to update the permissions, without
file system changes.

Reviewed-by: Matheus Castanho <msc@linux.ibm.com>