[$] An end to implicit fall-throughs in the kernel

The C switch statement has, since the beginning of the language,required the use of explicit break statements to prevent executionfrom falling through from one case to the next. This behavior canbe a useful feature, allowing for more compact code, but it can also leadto bugs. The effort to rid the kernel of implicit fall-through codingpatterns came to a conclusion with the 5.3-rc2 release, wherethe last cases were fixed. There is a good chance that these fixes willhave to be redone in the future, though.