When running airsnort you need wlanctl-ng which is found in linux-wlan-ng. It also seems to depend on some kernel support.
Airsnort does not actually depend on linux-wlan-ng, because it can easily be used by people using the orinoco_cs drivers. No reason to force people to install linux-wlan-ng if they use those drivers. I'll add a note at the end of the ebuild about linux-wlan-ng support for clarity.