CVE-2026-74676: vt: add permission check for KDSKBMETA ioctl

In the Linux kernel, the following vulnerability has been resolved:

vt: add permission check for KDSKBMETA ioctl

KDSKBMETA modifies keyboard meta mode but lacks the !perm check that all other keyboard setter ioctls in vtkioctl() enforce, allowing a process to change meta mode on a non-controlling console without authorization.