No dep8 tests for Ubuntu-specific default sysctl.d changes

[Robie Basak]

In bug 2003027, Ubuntu's procps regressed the default qdisc from fq_codel to pfifo_fast. Given that this was considered important enough to justify changing behaviour in a stable release, we should have an autopkgtest that verifies our intended delta against upstream, but we do not.

I appreciate that it's tricky to write a test that might need a VM to pick up kernel defaults to fully validate this, but we could at least have an autopkgtest that ensures that /etc/sysctl.d/ contains the expected net.core.default_qdisc setting and not any duplicate settings. You could also include checks for anything else that is Ubuntu-specific in there.