windows os - Close and minimize button behavior for my desktop application

I am developing a desktop application that will run on user's PC in background(system tray). User won't have to start the app as it starts with the system. Basically this app listens to a port and waiting for http request. Users will be able to change the port(rare case) by clicking the application's system tray icon. Here is the screenshot:

I don't want the users to close the app accidentally. Should I use the close button as minimize to system tray or the minimize button itself?

Edit: Users can quit the app by system tray icon's menu. Like: Skype.

n.b. I disabled the maximize button as the window size is fixed.