smbd: use fsp_get_pathref_fd() for fstat() calls

smbd: use fsp_get_pathref_fd() for fstat() calls

If we can access the path to a file, by default we have FILE_READ_ATTRIBUTES
from the containing directory. See the section: "Algorithm to Check Access to an
Existing File" in MS-FSA.pdf.

So it's also safe to use a root opened pathref fd, as the root open is done on
the final component after a chdir() to the parent directory was done while still
impersonating the use. Qed.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>