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/src/timer.c b/src/timer.c
index 37d7d16..9b2dd9e 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -20,7 +20,7 @@
 
 #include <assert.h>
 #include <string.h>
-#include <osmocore/timer.h>
+#include <osmocom/core/timer.h>
 
 static LLIST_HEAD(timer_list);
 static struct timeval s_nearest_time;