Prepare for devlink reload being called with devlink->lock held and
convert the netdevsim driver to use unlocked devlink API during init and
fini flows. Take devl_lock() in reload_down() and reload_up() ops in the
meantime before reload cmd is converted to take the lock itself.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>