devlink: Refactor devlink_rate_nodes_check

devlink: Refactor devlink_rate_nodes_check

devlink_rate_nodes_check() was used to verify there are no devlink rate
nodes created when switching the esw mode.

Rate management code is about to become more complex, so refactor this
function:
- remove unused param 'mode'.
- add a new 'rate_filter' param.
- rename to devlink_rates_check().
- expose devlink_rate_is_node() to be used as a rate filter.

This makes it more usable from multiple places, so use it from those
places as well.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260128112544.1661250-6-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>