android: use onSuccess parameter in setWantRunning (#516)

Previously we were never actually invoking this parameter
We previously weren't setting vpnActive after closing IPNService

Updates tailscale/corp#22284

Signed-off-by: kari-ts <kari@tailscale.com>

android/src/main/java/com/tailscale/ipn/App.kt

@@ -160,7 +160,7 @@ class App : UninitializedApp(), libtailscale.AppContext, ViewModelStoreOwner {
   fun setWantRunning(wantRunning: Boolean, onSuccess: (() -> Unit)? = null) {
     val callback: (Result<Ipn.Prefs>) -> Unit = { result ->
       result.fold(
-          onSuccess = {},
+          onSuccess = { onSuccess?.invoke() },
           onFailure = { error ->
             Log.d("TAG", "Set want running: failed to update preferences: ${error.message}")
           })