Bluetooth: L2CAP: Fix response to L2CAP_ECRED_CONN_REQ

Similar to 03dba9c ("Bluetooth: L2CAP: Fix not responding with
L2CAP_CR_LE_ENCRYPTION") the result code L2CAP_CR_LE_ENCRYPTION shall
be used when BT_SECURITY_MEDIUM is set since that means security mode 2
which mean it doesn't require authentication which results in
qualification test L2CAP/ECFC/BV-32-C failing.

Link: bluez/bluez#1871
Fixes: 15f02b9 ("Bluetooth: L2CAP: Add initial code for Enhanced Credit Based Mode")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: Vudentz

net/bluetooth/l2cap_core.c

@@ -5112,7 +5112,8 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 
 	if (!smp_sufficient_security(conn->hcon, pchan->sec_level,
 				     SMP_ALLOW_STK)) {
-		result = L2CAP_CR_LE_AUTHENTICATION;
+		result = pchan->sec_level == BT_SECURITY_MEDIUM ?
+			L2CAP_CR_LE_ENCRYPTION : L2CAP_CR_LE_AUTHENTICATION;
 		goto unlock;
 	}