ecore_con: move Ecore_Con_Dns_Cb back to C

ecore_con: move Ecore_Con_Dns_Cb back to C

We'll be removing function pointer support from Eolian, instead
replacing any callback we can with events (arbitrary callbacks are
very difficult to support in bindings). As we'll be handling all
callbacks at once, we'll do this one at that point as well.