Ensure we benefit from new security features in Linux 4.14

https://outflux.net/blog/archives/2017/11/14/security-things-in-linux-v4-14/

As usual, some of it might need to be enabled on our side, and some of it might require changes in Debian’s src:linux. So as usual I’ll go through this and will file bug reports in Debian and here as needed.

Feature Branch: feature/15309-linux-4.15

Related issues

• Related to #14976 (closed)
• Blocked by #15309 (closed)

Original created by @intrigeri on 15000 (Redmine)