Upgrade Linux to 4.12

Originally created by @intrigeri on #12732 (Redmine)

Linux 4.11 is now in Debian testing. It’s likely it (or 4.12) will make it into stretch-backports in time for Tails 3.2. Let’s get ready for it.

Feature Branch: feature/12732-linux-4.12

Edited May 15, 2020 by intrigeri

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