netcfStateInitialize() initializes the driverState variable,
and when netcfStateCleanup is called, it will call virReportError()
if driverState is NULL.
This is not consistent with what other state objects are doing,
they return -1 without reporting an error in such cases.

See also
https://www.redhat.com/archives/libvir-list/2013-October/msg00809.html:

On Thu, Oct 17, 2013 at 01:40:19PM +0100, Daniel P. Berrange wrote:
> We don't want virStateCleanup to skip execution if virStateInitialize
> has failed though - every callback in virStateCleanup should be written
> to be safe if its corresponding init function hasn't run.