Well, I just watched this video from FOSDEM 2014, and it made me think about Genode. http://video.fosdem.org/2014/AW1121/Sunday/PicoTCP.webm or https://www.youtube.com/watch?v=AO4liMJZ0Qg
The FOSDEM page: https://fosdem.org/2014/schedule/event/deviot03/
The PicoTCP page on the company web site: http://www.tass.be/en-gb/expertise/connected-devices/picotcp/ which does have a link to the GNU GPL v.2 code: https://github.com/tass-belgium/picotcp
I really don't have the knowledge to compare with IwIP, but am pretty sure there is someone here able to evaluate how well it fits with Genode.