Updates to support new TrafficProfiles that require a user-specified Direction in the GateSpec

Currently the IGateSpec interface does not define a method to update the Direction field. So the implementation class GateSpec does not support such an update.

As a result, logic in the PacketcableProvider decouples the Direction field from the GateSpec in a request object and manages it separately to support corrective tests for a DOCSISServiceClassNameTrafficProfile.

This is ServiceClassName-specific logic that is not suitable for extension to support other types of TrafficProfiles.

I propose a small change to add a setter to the IGateSpec interface and corresponding implementation. This will allow the logic that supports the ServiceClassName-to-Direction mapping in the PacketcableProvider class to be modified in a contained scope relevant only to it's required behaviors. Additional Traffic Profiles can then be added to PacketcableProvider more easily.