Turn off DUN connection after tethering.

Use matching feature type when turning tethering off or the request is ignored.

Also, turn on DUN apn right away so that we don't fail aggressive test cases.

Also don't report connections for enabled apn's that we're no longer connected to.

bug:3332880
bug:3338033
Change-Id: I7db2dfd4879f03465bc9f6d39488c078570dcaf3