Documentation: devlink: extend reload-reinit description

Be more explicit about devlink entities that may stay and that have to
be removed during reload reinit action.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>