Update VPN preference state after disallow configuring VPN policy has changed.

1. When Settings > More and change disallow configuring VPN policy
   and resume Settings, update VPN preference state.

2. When Settings > More > VPN and change disallow configuring VPN policy
   and resume VPN Settings, update its state.

Test: manual

Signed-off-by : Sungmin Lee <insight.lee@lge.com>

Change-Id: I4f3c85733ca6ba05cba46e2f4854f54a42b10c21

src/com/android/settings/vpn2/VpnSettings.java

@@ -164,6 +164,7 @@ public class VpnSettings extends RestrictedSettingsFragment implements
     public void onResume() {
         super.onResume();
 
+        mUnavailable = mUserManager.hasUserRestriction(UserManager.DISALLOW_CONFIG_VPN);
         if (mUnavailable) {
             // Show a message to explain that VPN settings have been disabled
             if (!isUiRestrictedByOnlyAdmin()) {
@@ -172,6 +173,7 @@ public class VpnSettings extends RestrictedSettingsFragment implements
             getPreferenceScreen().removeAll();
             return;
         } else {
+            setEmptyView(getEmptyTextView());
             getEmptyTextView().setText(R.string.vpn_no_vpns_added);
         }