Wait for Berghain request body
    
    Berghain would sometimes not receive the request body from HAProxy,
    causing repeated challenges. Allow HAProxy to wait until the full
    body has arrived before proceeding to mitigate this.
    Note this is only a maximum time, HAProxy will also proceed sooner
    once the full body arrived.
    
    Link: https://github.com/DropMorePackets/berghain/issues/42
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>