MFC r329525:

Correct/improve the descriptions if kern.ipc.(shmsegs,sema,msqids).

The description of kern.ipc.shmsegs was wrong since 2005. I updated the
others (which were more correct) to match.

PR: 225933
Reviewed by: cem
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D14391