Deduplicate endpoints for ingress that has port defined

[StrongMonkey]

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In case of NLB port allocation, the service.status.ingress already have ports allocated. So we shouldn't need to read ports from service.spec.ports, as it will cause duplicated endpoints. So, deduplicate the endpoints to make sure each endpoint is unique

acorn-io/aws-load-balancer-controller#2

Related issue: https://github.com/acorn-io/manager/issues/1568 https://github.com/acorn-io/manager/issues/1567

[thedadams]

nit to avoid multiple allocations:

Suggested change

	var result []v1.Endpoint
	result := make([]v1.Endpoint, 0, len(set))