Include a grsecurity-patched kernel

Originally created by @ioerror on #7649 (Redmine)

Debian now has a grsec protected kernel.

• Historical perspective on it: https://bugs.debian.org/605090
• https://wiki.debian.org/grsecurity

Blueprint: https://tails.boum.org/blueprint/kernel_hardening/

Feature Branch: feature/7649-grsec

Subtasks

• #8600 (closed)
• #8602 (closed)
• #8604 (closed)
• #8605 (closed)
• #8606 (closed)
• #12104 (closed)
• #12107 (closed)
• #12110 (closed)

Related issues

• Related to #10040 (closed)
• Blocked by #10298 (closed)