doc/man: supplant "wsync" with "nowsync" as the default

doc/man: supplant "wsync" with "nowsync" as the default

Change the default from "wsync" to "nowsync". "nowsync" has been the
default since kernel version 5.16.

This information was reported on
https://pad.ceph.com/p/Report_Documentation_Bugs by Benjamin Mare on 07
Oct 2024.

The commit relevant to this change can be seen here, in Linus's main
branch:
https://github.com/torvalds/linux/commit/f7a67b463fb83a4b9b11ceaa8ec4950b8fb7f902

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 9f0af5d75dc64ef0520fd78f29815d2a824a859b)