queue(3): Install *_SPLIT_AFTER() links to the main manual page

Completes commit "queue(3): New *_SPLIT_AFTER(), *_ASSERT_EMPTY(),
*_ASSERT_NONEMPTY()" (c02880233949b01f).

MFC after: 1 day
Sponsored by: The FreeBSD Foundation

(cherry picked from commit c071616b06aa0f51ac4314f989c472d0268c2ddb)