Add new BSC RLL layer of code

A caller can call rll_establish(lchan, link_id) and a callback to the GSM RLL
code.  He will get called back if the RLL link is established or receives some
error message, or the establishment times out.

We need this for proper SMS implementation, where we need to restablish a SAPI3
RLL link before transmitting the actual CP-DATA messages.
diff --git a/openbsc/include/openbsc/bsc_rll.h b/openbsc/include/openbsc/bsc_rll.h
new file mode 100644
index 0000000..b2898d1
--- /dev/null
+++ b/openbsc/include/openbsc/bsc_rll.h
@@ -0,0 +1,19 @@
+#ifndef _BSC_RLL_H
+#define _BSC_RLL_H
+
+#include <openbsc/gsm_data.h>
+
+enum bsc_rllr_ind {
+	BSC_RLLR_IND_EST_CONF,
+	BSC_RLLR_IND_REL_IND,
+	BSC_RLLR_IND_ERR_IND,
+	BSC_RLLR_IND_TIMEOUT,
+};
+
+int rll_establish(struct gsm_lchan *lchan, u_int8_t link_id,
+		  void (*cb)(struct gsm_lchan *, u_int8_t, void *,
+			     enum bsc_rllr_ind),
+		  void *data);
+void rll_indication(struct gsm_lchan *lchan, u_int8_t link_id, u_int8_t type);
+
+#endif /* _BSC_RLL_H */