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

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

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

man3/malloc_info.3

@@ -60,6 +60,19 @@ was nonzero.
 .SH VERSIONS
 .BR malloc_info ()
 was added to glibc in version 2.10.
+.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 malloc_info ()
+T}	Thread safety	MT-Safe
+.TE
+
 .SH CONFORMING TO
 This function is a GNU extension.
 .SH NOTES