RT-1.15: Reduce OTG learned-prefix and route overhead

[jjw-a-0617]

Limit learned-prefix collection to port4 and use counted route ranges for IPv4 advertisements.

This reduces OTG resource usage while preserving test settings.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request optimizes OTG resource usage in BGP scale tests by refining how learned prefixes are filtered and how routes are advertised. By limiting prefix collection to specific ports and switching to counted route ranges, the test suite becomes more efficient while maintaining existing test coverage.

Highlights

• Learned Information Filtering: Restricted learned-prefix collection to only occur on 'port4' to reduce resource overhead.
• Route Advertisement Optimization: Replaced individual prefix iterations with counted route ranges for IPv4 advertisements to improve performance.
• Code Refactoring: Introduced a helper function for adding BGP communities to simplify route configuration logic.

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[OpenConfigBot]

Pull Request Functional Test Report for #5764 / 579bbf9

Virtual Devices

Device	Test	Test Documentation	Job	Raw Log
Arista cEOS		RT-1.15: BGP Addpath on scale with and without routing policy
Cisco 8000E		RT-1.15: BGP Addpath on scale with and without routing policy
Cisco XRd		RT-1.15: BGP Addpath on scale with and without routing policy
Juniper ncPTX		RT-1.15: BGP Addpath on scale with and without routing policy
Nokia SR Linux		RT-1.15: BGP Addpath on scale with and without routing policy
Openconfig Lemming		RT-1.15: BGP Addpath on scale with and without routing policy

Hardware Devices

Device	Test	Test Documentation	Raw Log
Arista 7808		RT-1.15: BGP Addpath on scale with and without routing policy
Cisco 8808		RT-1.15: BGP Addpath on scale with and without routing policy
Juniper PTX10008		RT-1.15: BGP Addpath on scale with and without routing policy
Nokia 7250 IXR-10e		RT-1.15: BGP Addpath on scale with and without routing policy

Help

[gemini-code-assist]

Code Review

This pull request refactors the BGP scale test by restricting the learned information filters to 'port4' and replacing dynamic IPv4 prefix generation with hardcoded ranges and counts. It also introduces a helper function to simplify adding BGP communities. The reviewer identified a critical issue where the lack of explicit increment steps for the route ranges causes OTG to default to '0.0.0.1', resulting in overlapping subnets and fewer advertised prefixes than expected. Suggestions were provided to set appropriate step values for each prefix length.