lib: SCO voice setting support header

Modify headers to enable support for changing SCO voice setting.
Corresponding commit implements functionality on kernel side.

Author: Frédéric Dalleau

lib/bluetooth.h

@@ -104,6 +104,14 @@ struct bt_security {
  */
 #define BT_CHANNEL_POLICY_AMP_PREFERRED		2
 
+#define BT_VOICE		11
+struct bt_voice {
+	uint16_t setting;
+};
+
+#define BT_VOICE_TRANSPARENT			0x0003
+#define BT_VOICE_CVSD_16BIT			0x0060
+
 /* Connection and socket states */
 enum {
 	BT_CONNECTED = 1, /* Equal to TCP_ESTABLISHED to make net code happy */