SDK 13 Alpha
The header guard in serialization/connectivity/codecs/s132_s140/serializers/ble_l2cap_conn.h
looks like this:
#ifndef BLE_L2CAP_CONN_H__
#define BLE_L2CAP_CON__H__
Note the change in spelling between the two lines. The second line should get an extra N instead of an underscore.