Bluetooth: Fix ignoring debug keys in mgmt_load_link_keys

We should never allow user space to feed back debug keys to the kernel.
If the user desires to use debug keys require setting the appropriate
debug keys mode and performing a new pairing.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>