This is a follow-up to: containernetworking/cni#1061

The route table ID can now be specified using the CNI Spec v1.1 and the Source Based Routing documentation mentions a potential enhancement to pass the table number as an input.
https://www.cni.dev/plugins/current/meta/sbr/#future-enhancements-and-known-limitations

Here is the expected behavior with this change:

• Using the option to set the table number in the SBR meta plugin, a policy route will be created for each IP added for the interface returned by the main plugin. Unlike the default behavior, the routes will not be moved to the table.
• The default behavior (table ID not set) will be kept.

I would like to implement it, I will open a PR once #1021 gets merged.