Bluetooth: Controller: Use BT_HCI_ERR_UNSPECIFIED as needed

A Host shall consider any error code that it does not
explicitly understand equivalent to the error code
Unspecified Error (0x1F).

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>
(cherry picked from commit 78466c8)
Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

subsys/bluetooth/controller/hci/hci.c

@@ -8516,7 +8516,7 @@ static void encrypt_change(uint8_t err, uint16_t handle,
 	hci_evt_create(buf, BT_HCI_EVT_ENCRYPT_CHANGE, sizeof(*ep));
 	ep = net_buf_add(buf, sizeof(*ep));
 
-	ep->status = err;
+	ep->status = err ? err : (encryption_on ? err : BT_HCI_ERR_UNSPECIFIED);
 	ep->handle = sys_cpu_to_le16(handle);
 	ep->encrypt = encryption_on ? 1 : 0;
 }