Bluetooth: Track discovery type

This patch adds to struct discovery_state the field 'type' so that
we can track the discovery type the device is performing.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>