AMR->IuUP: do not crash on AMR data before IuUP Init

When translating AMR to IuUP, when AMR data arrives before the IuUP side
has negotiated an IuUP Initialization, do not crash osmo-mgw, but return
failure and drop the AMR packet.

As soon as IuUP Initialization occured and RFCIs are defined, the AMR
starts to pass through to the IuUP side.

Related: SYS#5092
Change-Id: Id9efb7e523d8d9af988e4bf4f5e925839204f934

src/libosmo-mgcp/mgcp_iuup.c

@@ -98,7 +98,11 @@ static int8_t _conn_iuup_amr_ft_2_rfci(struct mgcp_conn_rtp *conn_rtp, uint8_t f
 	uint8_t rfci_cnt = 0;
 	unsigned match_bytes = (unsigned)osmo_amr_bytes(ft);
 	struct osmo_iuup_rnl_prim *irp = conn_rtp->iuup.init_ind;
-	OSMO_ASSERT(irp);
+	if (!irp) {
+		/* No IuUP Initialization has occured on the IuUP side yet. Return error and drop the RTP data, until
+		 * the IuUP Initialization has configured the link. */
+		return -1;
+	}
 
 	/* TODO: cache this somehow */
 	for (i = 0; i < ARRAY_SIZE(irp->u.status.u.initialization.rfci); i++) {