include: reorganize headers file to include/osmocom/[gsm|core]

This patch moves all GSM-specific definitions to include/osmocom/gsm.
Moreover, the headers in include/osmocore/ have been moved to
include/osmocom/core.

This has been proposed by Harald Welte and Sylvain Munaunt.

Tested with `make distcheck'.

Signed-off-by: Pablo Neira Ayuso <pablo@gnumonks.org>
diff --git a/tests/timer/timer_test.c b/tests/timer/timer_test.c
index 1b458d8..30b08ad 100644
--- a/tests/timer/timer_test.c
+++ b/tests/timer/timer_test.c
@@ -20,8 +20,8 @@
 
 #include <stdio.h>
 
-#include <osmocore/timer.h>
-#include <osmocore/select.h>
+#include <osmocom/core/timer.h>
+#include <osmocom/core/select.h>
 
 #include "../../config.h"