libnvdimm, namespace: do not delete namespace-id 0

libnvdimm, namespace: do not delete namespace-id 0

commit 9d032f4201d39e5cf43a8709a047e481f5723fdc upstream.

Given that the naming of pmem devices changes from the pmemX form to the
pmemX.Y form when namespace id is greater than 0, arrange for namespaces
with id-0 to be exempt from deletion. Otherwise a simple reconfiguration
of an existing namespace to a new mode results in a name change of the
resulting block device:

    # ndctl list --namespace=namespace1.0
    {
      "dev":"namespace1.0",
      "mode":"raw",
      "size":2147483648,
      "uuid":"3dadf3dc-89b9-4b24-b20e-abc8a4707ce3",
      "blockdev":"pmem1"
    }

    # ndctl create-namespace --reconfig=namespace1.0 --mode=memory --force
    {
      "dev":"namespace1.1",
      "mode":"memory",
      "size":2111832064,
      "uuid":"7b4a6341-7318-4219-a02c-fb57c0bbf613",
      "blockdev":"pmem1.1"
    }

This change does require tooling changes to explicitly look for
namespaceX.0 if the seed has already advanced to another namespace.

Fixes: 98a29c39dc68 ("libnvdimm, namespace: allow creation of multiple pmem-namespaces per region")
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>