vn_fullpath.9: Add missing links for described functions

To reflect all the functions that are now described in the manual page.

Fixes: 9f269a0a771a ("MAC/do: Check executable path ...")
MFC after: 3 days
Event: EuroBSDCon 2025
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 05e5de00b9ea048f868522ff0bdae4e388685ddf)
(cherry picked from commit c87a9f51a0debf707cb4fc9a5e3b4425b08d154d)

(Compilation fix MFCed in the same commit.)