Unable to set initcwnd on a Hetzner server

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http://serverfault.com – We just ordered a bunch of Hetzner EX40SSD servers with the minimal Debian install image that they provide and everything is just fine except that looking at tcpdumps for fine tuning the network from various locations the initcwnd param seems to be stuck at 6 no matter how we change it. By default Debian 3.2 kernels should have that setting to 10 so it's pretty strange. Is it possible that the NIC driver or a custom setting in the Hetzner Debian image is limiting this param? Even if we set it to 4, like the old kernel default, it doesn't work. Any ideas would be much appreciated! Does anyone (HowTos)