BACKPORT: posix_acl: Clear SGID bit when setting file permissions

(cherry pick from commit 07393101)

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

NB: conflicts resolution included extending change to ext3 driver.
    We did not resolve the ACL leak in this CL, require additional
    upstream fixes.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Bug: 32458736
Change-Id: I19591ad452cc825ac282b3cfd2daaa72aa9a1ac1