After a reboot everything went back to a non-working state.. Booting with brcmfx-driver=1 fails the initialisation of a driver, brcmfx-driver=2 boots OK, but wifi is disabled. I guess I am not competent enough to figure out what I did right the first time, so maybe someone could help?
debug_4217.zip
UPDATE: recreated the steps that I did last time and everything works again (not for long I guess). I had to remove AirportBrcmFixup.kext, rebuild cache, reboot, install AirportBrcmFixup.kext again and reboot 2 times (first time the system halted at boot with message "AirportBrcmFixup: init @ failed to call parent 6", second time it booted OK). I am so confused.. but it works.