[Wi-Fi] Can't change EAP method for a saved enterprise Wi-Fi network

Should only allow saved network UI initialization for once.

Bug: 140362368
Test: WifiConfigControllerTest
      manual:
      Manually change EAP method and other security fields for a saved
      Wi-Fi neterprise network.

Change-Id: Iddc1dae53849760f43b41b75262358dff6ba09af
Merged-In: Iddc1dae53849760f43b41b75262358dff6ba09af