network: keep track of radio buttons in connection editor with action

Hooking to all the toggled signals from all the buttons for executing
the same action is inneficient, and can potenticall end up in a segmentation
 fault due to some race in the signal emmission, where the active button
 gets deactivated before the clicked button is activated

Looking at the GTK4 code, in a radio group:

- The button which was previously active gets de-activated, emitting its
corresponding toggled signal.
- The active property for the clicked button gets set.
- The clicked button emits its toggled signal.

Therefore, if the first toggle signal gets processed before the active
property is set, there can be a race condition. We are seeing this downstream
at pmOS: https://gitlab.com/postmarketOS/pmaports/-/issues/1816

Instead of this racy behavior, follow upstream recommendation and keep track
of the state through a stateful signal.