Add missing sysctl entries to conf file
Make sure sysctl settings are reset to default after each test
Link hardening is upstream in recent kernels

Don't expose the sysctl entries of features that we don't support, either because 1) the kernel is too old to do the proection, or 2) the protection already exists in the kernel. I don't want to maintain duplicate functionality, and see these extras going into the mainline as a good thing.