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/src/gprs/sgsn_vty.c b/src/gprs/sgsn_vty.c
index cf44cc4..3a5b2ca 100644
--- a/src/gprs/sgsn_vty.c
+++ b/src/gprs/sgsn_vty.c
@@ -48,7 +48,7 @@
 #include "../../bscconfig.h"
 
 #ifdef BUILD_IU
-#include <openbsc/iu.h>
+#include <osmocom/ranap/iu_client.h>
 #endif
 
 static struct sgsn_config *g_cfg = NULL;
@@ -291,7 +291,7 @@
 		vty_out(vty, " no compression v42bis%s", VTY_NEWLINE);
 
 #ifdef BUILD_IU
-	iu_vty_config_write(vty, " ");
+	ranap_iu_vty_config_write(vty, " ");
 #endif
 
 	return CMD_SUCCESS;
@@ -1285,7 +1285,7 @@
 	install_element(SGSN_NODE, &cfg_comp_v42bisp_cmd);
 
 #ifdef BUILD_IU
-	iu_vty_init(SGSN_NODE, &g_cfg->iu.rab_assign_addr_enc);
+	ranap_iu_vty_init(SGSN_NODE, &g_cfg->iu.rab_assign_addr_enc);
 #endif
 	return 0;
 }