netdevsim: Protect both reload_down and reload_up paths

Don't progress with adding and deleting ports as long as devlink
reload is running.

Fixes: 23809a72 ("netdevsim: Forbid devlink reload when adding or deleting ports")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>