Bluetooth: Limit userspace exposure of stack internal events

The stack internal events that are exposed to userspace should be
limited to HCI_DEV_REG, HCI_DEV_UNREG, HCI_DEV_UP and HCI_DEV_DOWN.

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