Added unmetered use only data connection support

If a data network is brought up while data is turned off because
the request APN is unmetered, when data is enabled again, this data
network needs to be torn down so a full capable data network can
be re-established.

Test: Unit tests
bug: 30936226
Change-Id: Ia233c80fa14980713bfe66bef61f1c6f4a8c1c0d