nvme-fabrics: fix kato initialization

Currently kato is initialized to NVME_DEFAULT_KATO for both
discovery & i/o controllers. This is a problem specifically
for non-persistent discovery controllers since it always ends
up with a non-zero kato value. Fix this by initializing kato
to zero instead, and ensuring various controllers are assigned
appropriate kato values as follows:

non-persistent controllers  - kato set to zero
persistent controllers      - kato set to NVMF_DEV_DISC_TMO
                              (or any positive int via nvme-cli)
i/o controllers             - kato set to NVME_DEFAULT_KATO
                              (or any positive int via nvme-cli)

Signed-off-by: Martin George <marting@netapp.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>