dpkg-dev should not actually be required for a proper dkms build of zfs. Commit fe51ab5f2 (already on salsa/master) just adds a dependency, if we use commit a99df746d (from [1]), we can avoid a dependency, making for a cleaner package.
[1] https://salsa.debian.org/zfsonlinux-team/zfs/merge_requests/9
