Bluetooth: Add macros for filter duplicates values

This patch adds macros for filter_duplicates parameter values from
HCI LE Set Scan Enable command. It also fixes le_scan_enable_req
function so it uses the LE_SCAN_FILTER_DUP_ENABLE macro instead of
a magic number.

The LE_SCAN_FILTER_DUP_DISABLE was also defined since it will be
required to properly support the GAP Observer Role.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 3f4266b..84c37ab 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -998,6 +998,8 @@
 
 #define LE_SCANNING_DISABLED		0x00
 #define LE_SCANNING_ENABLED		0x01
+#define LE_SCAN_FILTER_DUP_DISABLE	0x00
+#define LE_SCAN_FILTER_DUP_ENABLE	0x01
 
 #define HCI_OP_LE_SET_SCAN_ENABLE	0x200c
 struct hci_cp_le_set_scan_enable {