BugLink: http://bugs.launchpad.net/bugs/1566221

Allowing users to write to address space makes it possible for the kernel
to be subverted, avoiding module loading restrictions. Prevent this when
any restrictions have been imposed on loading modules.
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>