Cleanup connections for APNs that are not connected

- After disabling a network, ConnectivityService tears down
  the data connection
- However, for APNs that are in Connecting, Failed or Retry
  state, ConnectivityService will not do that because the NetworkAgent
  is created only when a DataConnection goes into Active State.
  Take care of this case by explicitly tearing down the data connection

CRs-Fixed: 914669

Change-Id: I87f286cb8b5fe5c6a33e8c5cf53da7bca8d7aa2b