Retrieve the ResponseCallback used to dispatch decoupled responses.
This may be either a new ResponseCallback created via the ClientBinding
or a preexisting instance, if the decoupled response endpoint is
being reused.
a ResponseCallback instance
Invoke on a two-way operation on the remote service. The transport
should provide a context that returns a valid InputStream containing
the response in one of two ways:
if tightly coupled, via the return value of this method
if decoupled, via the ResponseCallback
Parameters: context - containg in the request context containing resonse if tightly coupled, null otherwise