iu_client: introduce UE field free_on_release

Allow to free UE ctx when receiving a Iu Release Complete.
In preparation of ranap_iu_tx_release_free() it requires
a field to free the Iu ctx on it's own without depending
on the upstream user.

Change-Id: Iac41cd3cce3232d01b2f7ede0cc46226c2cfb6c0
diff --git a/include/osmocom/ranap/iu_client.h b/include/osmocom/ranap/iu_client.h
index a93fff3..24a5af9 100644
--- a/include/osmocom/ranap/iu_client.h
+++ b/include/osmocom/ranap/iu_client.h
@@ -31,6 +31,8 @@
 	struct gprs_ra_id ra_id;
 	enum ranap_nsap_addr_enc rab_assign_addr_enc;
 	bool notification; /* send notification to the upstream user */
+	/* if true the ue_ctx will be free on Iu release complete */
+	bool free_on_release;
 	/* Will be set when the Iu Release Command has been sent */
 	struct osmo_timer_list release_timeout;
 };