l2tpns hasn't been properly maintained in nearly a decade (maybe longer). Every version out there is some sort of unique branch of an evolutionary tree with no regard to version numbers nor dates. And it will likely crash in under 30 seconds, if it runs at all.
This is my update to l2tpns fixing numerous bugs, crashes, and other oddments. Every patch I could find has been integrated and its now running on modern linux 4.x kernel systems. If you use l2tpns, you should probably check this out. If you are maintaining l2tpns in your own repository, please update to this version and push any differences to me!