v2v: fix id naming of chapter 4

Somehow I forget to do this before pushing...

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
v2v: Chapter 5 done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
v2v: Chapter 6 done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
v2v: Chapter 7 done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
v2v: Appendix A done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
v2v: fix two xref TODOs

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>