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