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/write_queue.c b/src/write_queue.c
index 7295569..0642aad 100644
--- a/src/write_queue.c
+++ b/src/write_queue.c
@@ -21,7 +21,7 @@
  *
  */
 
-#include <osmocore/write_queue.h>
+#include <osmocom/core/write_queue.h>
 
 int write_queue_bfd_cb(struct bsc_fd *fd, unsigned int what)
 {