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/tests/timer/timer_test.c b/tests/timer/timer_test.c
index b06c774..9c51ad9 100644
--- a/tests/timer/timer_test.c
+++ b/tests/timer/timer_test.c
@@ -29,7 +29,7 @@
 #include <osmocom/core/select.h>
 #include <osmocom/core/linuxlist.h>
 
-#include "../config.h"
+#include "config.h"
 
 static void main_timer_fired(void *data);
 static void secondary_timer_fired(void *data);