Comment 17 for bug 144501

Instead of loading the module "mac80211", you can load the module "iwlwifi_mac80211"
Make sure you unload "mac80211" before loading "iwlwifi_mac80211"
So:
sudo modprobe -r ipw3945
sudo modprobe -r ieee80211
sudo modprobe -r ieee80211_crypt
sudo modprobe -r mac80211
sudo modprobe iwlwifi_mac80211
sudo modprobe iwl3945