ktrace: Fix an inverted privilege check

Approved by: so
Approved by: re (cperciva)
Security: FreeBSD-SA-24:06.ktrace
Security: CVE-2024-6760
Fixes: 1762f674ccb5 ("ktrace: pack all ktrace parameters into allocated structure ktr_io_params")

(cherry picked from commit 166b7573b5220aadf8b02a85933c9651b909b309)
(cherry picked from commit f702110bc4bcc593b38674ec6e4fadf6c4626432)