Fix all references to config.h

config.h is created in $(top_buildir)/config.h.
Let's make sure all CPPFLAGS add correct -Ipath includes,
and that all code includes the correct file.

Change-Id: Ie9ea38bb009bc715b01cde4d66d181f7bec2e7bd
diff --git a/src/vty/stats_vty.c b/src/vty/stats_vty.c
index 299ec24..f940018 100644
--- a/src/vty/stats_vty.c
+++ b/src/vty/stats_vty.c
@@ -21,7 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "../../config.h"
+#include "config.h"
 
 #include <osmocom/vty/command.h>
 #include <osmocom/vty/buffer.h>