tabline confused with tab and buffer
Sometime tabline show buffers:

![image](https://user-images.githubusercontent.com/3498786/114291157-c9c8ba00-9ab7-11eb-80ab-a275622c6296.png)

But sometimes tabline show tabs:

![image](https://user-images.githubusercontent.com/3498786/114291169-d64d1280-9ab7-11eb-9e9c-bfa30084edf4.png)

That made me confused, How can I set the default to show tabs, do not show buffers on the tabline just like other familiar editors.