Enforce restricted user, getConnectionOwnerUid checks

This CL adds checks to ensure restricted users cannot change or
start/stop platform VPNs. In addition, this also adds checks to the
ConnectivityManager#getConnectionOwnerUid() to ensure that only
VpnService based VPNs can identify connections

Bug: 148040659
Test: FrameworksNetTests run
Change-Id: Id47ada5766036bfc84f3ba47f66f2d2683af916d
5 files changed