man/man2/msgop.2: STANDARDS, HISTORY: Update POSIX appearances of msg{rcv,snd}(2)

man/man2/msgop.2: STANDARDS, HISTORY: Update POSIX appearances of msg{rcv,snd}(2)

msgrcv(2) and msgsnd(2) appeared in SUSv1.[1]  The functions were added
to POSIX.1-2001 when POSIX and SUS merged, but as an XSI extension
(still SUS-only).[2][3]  And they remain as an XSI extension in
POSIX.1-2024.[4][5]

[1] X/Open CAE Specification, System Interfaces and Headers Issue 4,
Version 2, Chapter 3 "System Interfaces", pp. 408-411.
[2] IEEE Std 1003.1-2001, Volume 2, Chapter 3 "System Interfaces", pp.
806-808.
<https://pubs.opengroup.org/onlinepubs/009604499/functions/msgrcv.html>
[3] IEEE Std 1003.1-2001, Volume 2, Chapter 3 "System Interfaces", pp.
809-811.
<https://pubs.opengroup.org/onlinepubs/009604499/functions/msgsnd.html>
[4] IEEE Std 1003.1-2024, Volume 2, Chapter 3 "System Interfaces", pp.
1475-1477.
<https://pubs.opengroup.org/onlinepubs/9799919799/functions/msgrcv.html>
[5] IEEE Std 1003.1-2024, Volume 2, Chapter 3 "System Interfaces", pp.
1478-1480.
<https://pubs.opengroup.org/onlinepubs/9799919799/functions/msgsnd.html>

Signed-off-by: Seth McDonald <sethmcmail@pm.me>
Message-ID: <86e7c24b14286fe05108c623d61d93106f9c9209.1769429341.git.sethmcmail@pm.me>
Signed-off-by: Alejandro Colomar <alx@kernel.org>