dynamic-routing-port-name option has no effect

[ Impact ]
When using the native OVN dynamic routing feature for learning routes, mapping from which interface a route is learned to a specific LRP is required. Failing to do this will create invalid routes in the system.

The dynamic-routing-port-name option was provided as means to do this, however a bug prevents this feature from working as intended.

Consequently using dynamic routing to learn routes does not work without this patch.

[ Test Plan ]
The main branch of MicroOVN makes use of this feature [2], and has thorough test suites validating operation. As a form of verification we will build a version of MicroOVN with the -proposed package and provide test results.

[ Where problems could occur ]
OVN 25.03 was the first version with native support for dynamic routing through the use of routing protocol suites such as BIRD or FRR.

As detailed above the route learning feautre is currently not usable, and the fix has been merged to main and backported to 25.09 and 25.03 branches.

Due to the feature currently being broken, the regression potential is minimal or non-existent.

[ Other Info ]
The dynamic-routing-port-name option was added to the Logical_Router_Port table [0] as means of selecting which LRPs should learn routes. When used together with Open_vSwitch external_ids:dynamic-routing-port-mapping, an LRP can also be mapped to a system interface as found in the system routing tables.

The description of the option states: "Only learn routes associated with the interface locally bound to the LSP or LRP specified here".

However, when an LR has LRPs with this option, learned routes are still associated with all LRPs of an LR [1].

In order for the option to work as documented there would have to be a check for whether any LRPs of an LR has this option, and if that is the case, only consider those LRPs.

0: https://manpages.ubuntu.com/manpages/questing/man5/ovn-nb.5.html#logical_router_port%20table
1: https://github.com/ovn-org/ovn/blob/db748328f36592f76c1ea991f0ea1b1ac79902b5/controller/route.c#L208
2: https://github.com/canonical/microovn/blob/624123ca227a136343b5e71c68d47f862654d3db/microovn/bgp/redirect.go#L293