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/core/utils.c b/src/core/utils.c
index 2012b74..231b65c 100644
--- a/src/core/utils.c
+++ b/src/core/utils.c
@@ -459,7 +459,7 @@
 	__attribute__((weak, alias("osmo_hexdump_nospc")));
 #endif
 
-#include "../config.h"
+#include "config.h"
 #ifdef HAVE_CTYPE_H
 #include <ctype.h>
 /*! Convert an entire string to lower case