introduce ue_context management

We keep one 'ue_context' structure for every UE that we see
a UE REGISTER REQUEST for.
diff --git a/src/hnbgw_hnbap.c b/src/hnbgw_hnbap.c
index cdd4895..d00d59e 100644
--- a/src/hnbgw_hnbap.c
+++ b/src/hnbgw_hnbap.c
@@ -23,6 +23,7 @@
 	return osmo_wqueue_enqueue(&ctx->wqueue, msg);
 }
 
+
 static int hnbgw_tx_hnb_register_acc(struct hnb_context *ctx)
 {
 	HNBRegisterAccept_t accept_out;
@@ -110,11 +111,14 @@
 	if (rc < 0)
 		return rc;
 
+	/* FIXME: convert UE identity into a more palatable format */
+	ue = ue_context_by_imsi("123");
+	if (!ue)
+		ue = ue_context_alloc(ctx, "123");
+
 	DEBUGP(DMAIN, "UE-REGSITER-REQ ID_type=%d cause=%ld\n",
 		ies.uE_Identity.present, ies.registration_Cause);
 
-	/* FIXME: convert UE identity into a more palatable format */
-
 	/* Send UERegisterAccept */
 	return hnbgw_tx_ue_register_acc(ue);
 }