move libiu to osmo-iuh/libosmo-ranap

Remove libiu here, use the functions from libosmo-ranap instead, by applying
the ranap_ / RANAP_ prefix.

Corresponding change-id in osmo-iuh.git is I6a3f7ad15be03fb94689b4af6ccfa828c25f45c0

To be able to run the msc_vlr tests for RAN_UTRAN_IU without Iu client headers
available, add iu_dummy.h, containing mere function signatures that match
iu_dummy.c and a mostly empty struct ranap_ue_conn_ctx.

Make sure we can build with and without --enable-iu: include osmo-iuh headers
only with --enable-iu.

Change-Id: Ib8c4fcdb4766c5e575618b95ce16dce51063206b
diff --git a/include/openbsc/gsm_data.h b/include/openbsc/gsm_data.h
index 43fc6d3..6079900 100644
--- a/include/openbsc/gsm_data.h
+++ b/include/openbsc/gsm_data.h
@@ -30,7 +30,7 @@
 struct bsc_subscr;
 struct vlr_instance;
 struct vlr_subscr;
-struct ue_conn_ctx;
+struct ranap_ue_conn_ctx;
 
 #define OBSC_LINKID_CB(__msgb)	(__msgb)->cb[3]
 
@@ -203,7 +203,7 @@
 
 	/* which Iu-CS connection, if any. */
 	struct {
-		struct ue_conn_ctx *ue_ctx;
+		struct ranap_ue_conn_ctx *ue_ctx;
 		uint8_t rab_id;
 	} iu;
 
@@ -493,7 +493,7 @@
 	struct {
 		/* CS7 instance id number (set via VTY) */
 		uint32_t cs7_instance;
-		enum nsap_addr_enc rab_assign_addr_enc;
+		int rab_assign_addr_enc;
 		struct osmo_sccp_instance *sccp;
 	} iu;