[$] Kernel regression tracking, part 2

The tracking of kernel regressions was discussed at the 2017 Kernel Summit; the topicmade a second appearance at the first-ever Maintainers Summit two dayslater. This session was partly a repeat of what came before for thebenefit of those (including Linus Torvalds) who weren't at the firstdiscussion, but some new ground was covered as well.