Privileged process monitoring via inverted detachment check

Improper privilege-transition handling in FreeBSD hwpmc allows local users to continue monitoring newly privileged processes. An inverted conditional in the hwpmc exec hook skips detaching performance-monitoring counters owned by an unprivileged process when execve loads a setuid or setgid image. Exploitation requires local access and a PMC attached before the credential transition; the result is continued observation of the privileged process, not control of it.