man: update recordsize max size info

Reflect https://github.com/openzfs/zfs/commit/f2330bd1568489ae1fb16d975a5a9bcfe12ed219
change in our man pages and add some context.

Wording is primarily copy-pasted from code comments.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: George Melikov <mail@gmelikov.ru>
Closes #16581