Bluetooth: Use HCI_MGMT instead of HCI_LINK_KEYS flag

Use HCI_MGMT flag instead of HCI_LINK_KEYS flag. There is a problem with
HCI_LINK_KEYS flag since it is set only when link keys are loaded. Otherwise
kernel assumes that old interface is used.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>