devlink: make sure driver does not read updated driverinit param before reload

The driverinit param purpose is to serve the driver during init/reload
time to provide a value, either default or set by user.

Make sure that driver does not read value updated by user before the
reload is performed. Hold the new value in a separate struct and switch
it during reload.

Note that this is required to be eventually possible to call
devl_param_driverinit_value_get() without holding instance lock.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>