Revert https://svnweb.freebsd.org/changeset/base/359809

The intended change was
sp->next.tqe_next = NULL;
sp->next.tqe_prev = NULL;
which doesn't fix the issue I'm seeing and the committed fix is
not the intended fix due to copy-and-paste.

Thanks a lot to Conrad Meyer for making me aware of the problem.

Reported by: cem