lisa._kmod: Add info on split BTF issue

Mismatching split BTF loading issue:
https://lore.kernel.org/all/YfK18x%2FXrYL4Vw8o@syu-laptop/t/#md877c45455918f8c661dc324719b91a9906dc7a3
https://bugzilla.opensuse.org/show_bug.cgi?id=1194501

has been fixed in:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=5e214f2e43e4

When that config is enabled: MODULE_ALLOW_BTF_MISMATCH=y

Unfortunately, that is not the default so keep LISA's current behavior.