Implement ServiceEndpoint.EndpointBehaviors

Implement ServiceEndpoint.EndpointBehaviors

This follows the reference source in understanding `EndpointBehaviors` to be an alias of `Behaviors` with a more general type.

Note that although an alias might not seem necessary to implement, when using netstandard1.3 the [`System.ServiceModel.Primitives`](https://www.nuget.org/packages/System.ServiceModel.Primitives) package exposes `EndpointBehaviors` but not `Behaviors`.