rangelock: Disable cheat mode by default

Cheat mode is incompatible with code which locks multiple ranges in the
same vnode, with at least one range being write-locked. This can arise
in kern_copy_file_range(). Until that's handled somehow, avoid the
problem to make the fusefs tests stable.

PR: 281073
Fixes: 9ef425e560a9 ("rangelocks: add fast cheating mode")
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D46457