Upgrade Linux to 4.15.0-2

Our devel branch FTBFS since Linux 4.15.0-1 was removed from sid. Let’s fix this on devel first and this will give us data points wrt. #15435 (closed).

Related issues

Blocks #13245 (closed)
Blocked by #15457 (closed)

Original created by @intrigeri on 15456 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information