fabrics: ensure zero kato for non-persistent controllers

fabrics: ensure zero kato for non-persistent controllers

Add a helper function that sets the default kato value for the
discovery controllers. Along with ensuring a non-zero kato value
(i.e. NVMF_DEF_DISC_TMO) is passed to a persistent discovery
controller, it also ensures a zero kato value is passed to a
non-persistent discovery controller, as mandated by the NVMe spec.

Signed-off-by: Martin George <marting@netapp.com>
[dwagner: ported from monolithic branch]
Signed-off-by: Daniel Wagner <dwagner@suse.de>