fcntl.2: The kernel source file mandatory.txt is now mandatory-locking.txt

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/fcntl.2

@@ -1101,11 +1101,14 @@ It is therefore inadvisable to rely on mandatory locking.
 .P
 See also
 .IR locks.txt ,
-.IR mandatory.txt ,
+.IR mandatory-locking.txt ,
 and
 .I dnotify.txt
 in the kernel source directory
 .IR Documentation/filesystems/ .
 (On older kernels, these files are directly under the
 .I Documentation/
-directory.)
+directory, and
+.I mandatory-locking.txt
+is called
+.IR mandatory.txt .)