Fix max body size limit

[mhamann]

Fixes #364

[rabbah]

given this is a fix for a previous fix is there a way to test this change as part of our ci?

[mhamann]

@rabbah there's an issue open to create a set of "integration-like" tests for the gateway, which I think is critical to the health of the codebase as things continue to evolve. I'm hoping to put a framework for that in place before the end of the year, and then build out missing test coverage over time. This test would definitely fall into that bucket.

I know there are some gateway tests in the main openwhisk repo, but I believe those should be geared more toward end-to-end scenarios.

Let me know if you have a different perspective on the problem.