staging: lustre: libcfs: double copy bug

The problem is that we copy hdr.ioc_len, we verify it, then we copy it
again without checking to see if it has changed in between the two
copies.

This could result in an information leak.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>