Switchyard JAXBTransformer does not honor MTOM attachment

Platform issue for https://issues.jboss.org/browse/SWITCHYARD-2866:

The JaxbTransformer does not currently resolve MTOM attachments We use this transformer to map between a SOAP binding and our bean which causes the @XmlMimeType field in our bean to always be null.

Setting xopExpand=true makes it work, but causes additional unwanted overhead. There should be a way to unmarshal the MTOM attachments without having to use xopExpand=true.