UDP round-robin load-balancing

[shaneutt]

Problem Statement

Previously we've added the ability to redirect UDP traffic to a Backend using eBPF, but only to a single Backend. The purpose of this task is to add support for multiple Backends in the Routing map, and then support to balance traffic between those Backends using the "round-robin" strategy in our eBPF data-plane code.

Prerequisites

• create the BACKEND data-structure and BACKENDS map #8
• TC program to redirect ingress traffic to a UDPRoute backend #9

Proposed Solution

• the BACKENDS map can now include multiple BACKEND resources
• the eBPF code is updated to handle load-balancing between BACKEND resources according to a round-robin strategy
• integration tests are added that provide a UDPRoute pointing to a Service results in the correct dispersion of requests across multiple BACKEND resources
• each UDPRoute should be able to support multiple BackendRefs
• each BackendRef for a UDPRoute should be able to support multiple Endpoints

Acceptance Criteria

• when a Service is used as a backendRef for a UDPRoute and it includes multiple endpoints, traffic is load-balanced between those endpoints with a basic round-robin strategy (future iterations may add other strategies, but not required to resolve this).

Note: for the purposes of this issue we do not need a complete/comprehensive/exhaustive implementation: we're targeting a basic "it works at a basic level" implementation for now so that PRs can be smaller and we can work iteratively forward.

[aryan9600]

i'd like to give this a shot :)

[mlavacca]

Thanks for your interest @aryan9600!

/assign @aryan9600