Get rid of small copmile warning

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3142 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_monitor.c

@@ -17,6 +17,7 @@
 #include <asterisk/monitor.h>
 #include <asterisk/app.h>
 #include <asterisk/utils.h>
+#include <asterisk/config.h>
 #include "../asterisk.h"
 #include "../astconf.h"