Bluetooth: Add hci_conn_lookup_type() helper function

Some drivers require knowledge of what connection handle is assigned
to what connection link type (ACL or SCO/eSCO). Instead of having each
driver implement connection tracking, provide a simple helper function
for lookup of the link type.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 2e08f5a..d5f85d7 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -274,6 +274,7 @@
 /* Low Energy links do not have defined link type. Use invented one */
 #define LE_LINK		0x80
 #define AMP_LINK	0x81
+#define INVALID_LINK	0xff
 
 /* LMP features */
 #define LMP_3SLOT	0x01