Enabling BTF in the kernel brakes kexec from pre-BTF kernel (e.g. when
upgrading from 1.2.x to 1.3.x).
As there's no way to detect Talos version in the installer at the
moment, use another way to detect whether BTF is enabled in the Talos
version which is running right now.
Fixes#6443
Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>
