Cleanup connections for APNs that are not connected

- After a network is disabled via releaseNetwork, 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. As
  a result, even if the client release the network request, the
  corresponding data connection is not torn down
- Take care of this case by explicitly tearing down the data connection

Test: Telephony sanity tests. QC tested with MMS app.
bug: 34756779
Change-Id: I87f286cb8b5fe5c6a33e8c5cf53da7bca8d7aa2b