Change ScrollView to NestedScrollView for wifi_dialog

After enabling collapsing toolbar, ScrollView is not working with
CoordinatorLayout. So we need to update it to NestedScrollView to make
it work with CoordinatorLayout.

Bug: 182221182
Test: make RunSettingsLibRoboTests ROBOTEST_FILTER=com.android.settingslib.wifi
      manual visual
      In Settings -< Network & internet -> Wi-Fi -> Add network,
      select enterprise type and scroll the screen.
Change-Id: Ie9de753ee198409275e818a123b5ba7f9b6a1e26