I bumped into this when trying to run two separate instances of direwolf. One for VHF and one for HF. In that case I would see a collision on port 8001. After digging around a bit I found that the way to turn off the 8001 default is to set KISSPORT 0 before any other KISSPORT settings in the config.?
I also proposed a code change to the KISSPORT default behavior here.
https://github.com/wb2osz/direwolf/pull/333