fabrics: fix passing ctrl_loss_tmo=0 by default

fabrics: fix passing ctrl_loss_tmo=0 by default

cfg.ctrl_loss_tmo will be cleared to zero even if it wasn't set
at all, we must not pass ctrl_loss_tmo in the connection string.

This fixes a regression caused by allowing ctrl_loss_tmo to be
zero at all, by setting it to be a sane default (which currently
matches the kernel default).

Fixes: a6105a30a39a ("nvme-cli/fabrics: Add tos param to connect cmd")
Fixes: 4b607779af71 ("Allow 0 value of ctrl_loss_tmo.")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>