mq_notify.3: ATTRIBUTES: Note function that is thread-safe

After research, We think mq_notify() is thread-safe. But, there
is not marking of mq_notify() in glibc document.
- mq_notify: MT-Safe

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/mq_notify.3

@@ -171,6 +171,19 @@ error if
 is NULL, and the caller is not currently registered to receive
 notifications for the queue
 .IR mqdes .
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lb lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.BR mq_notify ()
+T}	Thread safety	MT-Safe
+.TE
+
 .SH CONFORMING TO
 POSIX.1-2001.
 .SH NOTES