Add NetworkManagementInternal.isNetworkRestrictedForUid.

This will be used by the ActivityManagerService to decide if
an app needs to block for network or not.

Bug: 27803922
Test: runtest -c com.android.server.NetworkManagementInternalTest frameworks-services
      cts-tradefed run singleCommand cts-dev --module CtsHostsideNetworkTests -t com.android.cts.net.HostsideRestrictBackgroundNetworkTests
      and manual

Change-Id: I9e62406e2638f70497b43b5b41607df41aefd66c