Introduced in https://issues.apache.org/jira/browse/AMQ-3895
we use a prefetch value of 0 to ensure no dispatch till we get can receipt the sub. But we may need to find a better way.
Such that the prefetch values can be default on the way in and get applied by the broker.
Also, our default values should mirror the broker defaults based on destination and sub type, currently the all default to 1000.