netdevsim: implement proper devlink reload

During devlink reload, all driver objects should be reinstantiated with
the exception of devlink instance and devlink resources and params.
Move existing devlink_resource_size_get() calls into fib_create() just
before fib notifier is registered. Also, make sure that extack is
propagated down to fib_notifier_register() call.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>