regression requests on keep-alive HTTP connections only served after 40ms

The method `Libevent2TCPConnection.waitForData` only returns after 40ms.
In v0.7.17 I see `socket 11 write event (false)!` after `wait for data`. The write event  is missing on master.
I tried to bisect the issue but there were to many build errors in the git history to do so.