[$] Exported-symbol changes in 5.13

There have been many disagreements over the years in the kernel community
concerning 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 unintended
ways, and makes future changes harder. That said, there is no authority
overseeing 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 not
particularly hard to detect changes in symbol exports from one kernel
version to the next, and doing so can give some insights into the kinds of
changes that are happening under the hood.