Revert deleting the decryption error counters

[rincebrain]

Describe the feature would like to see added to OpenZFS

#12901 deleted the counters for decryption errors as "useless". Since I've personally had to ask people to run 2.1 several times now to see if their bug was a decryption error, I don't really agree.

How will this feature improve OpenZFS?

Since decryption errors are, like most of native encryption, janky and not well integrated into things like error reporting, at least having a counter to expose this happening would be useful still. (As it is, you get to guess from weird janky things like seeing errors reported without any R/W/CK incrementing, or hoping it didn't overflow the events backlog before they asked you...assuming it was even surfaced correctly.)

Additional context

#15267 and #15474 were recent cases where it was useful, #16147 is a case where it would have been useful but the user was running 2.2 so they couldn't use it, since it was deleted. #15837 was another case the user found it useful until they migrated to 2.2 and it was no longer there.