resolve typedef conflict from congestion_control_t

Resumes being able to build on old / esoteric gcc versions.

Fixes bug 40550; bugfix on 0.4.7.1-alpha.

mentioned in merge request !515 (closed)

requested review from @nickm

I would suggest that we not do it like this: the usual idea of how we structure _st.h headers is that we (try) to only include them from the C files that use them, so that we don't make structure internals visible in any place where it isn't necessary to do so.

Could you have a look at !517 (merged) and see if that approach works for you?

mentioned in issue #40550 (closed)

We got !517 (merged) working, so merged that instead.

closed