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_libgtp.c b/src/gprs/sgsn_libgtp.c
index 7ff8ece..90b4d16 100644
--- a/src/gprs/sgsn_libgtp.c
+++ b/src/gprs/sgsn_libgtp.c
@@ -52,7 +52,7 @@
 #include <openbsc/gprs_sndcp.h>
 
 #ifdef BUILD_IU
-#include <openbsc/iu.h>
+#include <osmocom/ranap/iu_client.h>
 #include <osmocom/ranap/ranap_ies_defs.h>
 #endif
 
@@ -548,7 +548,7 @@
 		} else {
 #ifdef BUILD_IU
 			/* Deactivate radio bearer */
-			iu_rab_deact(pctx->mm->iu.ue_ctx, 1);
+			ranap_iu_rab_deact(pctx->mm->iu.ue_ctx, 1);
 #else
 			return -ENOTSUP;
 #endif
@@ -687,7 +687,7 @@
 #ifdef BUILD_IU
 		/* Ignore the packet for now and page the UE to get the RAB
 		 * reestablished */
-		iu_page_ps(mm->imsi, &mm->p_tmsi, mm->ra.lac, mm->ra.rac);
+		ranap_iu_page_ps(mm->imsi, &mm->p_tmsi, mm->ra.lac, mm->ra.rac);
 
 		return 0;
 #else