mgcp: cancel transactions on timeout

when a transaction to the MGW times out, then the context
information is freed. Unfortunately the client is not informed
about this and will try to execute the callback anyway.

explicitly cancel the transaction in order to prevent access
to already freed data structures.

Change-Id: I40794dff7d10e2b6a96863a2da7e9fbd5662a1bf
diff --git a/include/osmocom/bsc/osmo_bsc_mgcp.h b/include/osmocom/bsc/osmo_bsc_mgcp.h
index e4b038c..7452513 100644
--- a/include/osmocom/bsc/osmo_bsc_mgcp.h
+++ b/include/osmocom/bsc/osmo_bsc_mgcp.h
@@ -21,6 +21,7 @@
 #pragma once
 
 #include <osmocom/mgcp_client/mgcp_common.h>
+#include <osmocom/mgcp_client/mgcp_client.h>
 
 /* MGCP state handler context. This context information stores all information
  * to handle the direction of the RTP streams via MGCP. There is one instance
@@ -48,6 +49,7 @@
 	struct gsm_lchan *lchan;
 	struct gsm_lchan *ho_lchan;
 	struct msgb *resp;
+	mgcp_trans_id_t mgw_pending_trans;
 };
 
 struct mgcp_ctx *mgcp_assignm_req(void *ctx, struct mgcp_client *mgcp, struct osmo_bsc_sccp_con *conn,