[$] Exported-symbol changes in 5.13

There have been many disagreements over the years in the kernel communityconcerning the exporting of internal kernel symbols to loadable modules.Exporting a symbol often exposes implementation decisions to outside code,makes it possible to use (or abuse) kernel functionality in unintendedways, and makes future changes harder. That said, there is no authorityoverseeing the exporting of symbols and no process for approving exports;discussions only tend to arise when somebody notices a change that they don't like. But it is notparticularly hard to detect changes in symbol exports from one kernelversion to the next, and doing so can give some insights into the kinds ofchanges that are happening under the hood.