mgw: rx_rtp(): reorder checks and handlings

First validate the origin of the message, then later the content
of the message and finally execute whatever triggers are necessary.
This way contents from unknown senders are not even parsed or acted
upon, avoiding useless potential harm.

Change-Id: I011a6d7d705768c32a35cec5cd7169725a21a670

src/libosmo-mgcp/mgcp_network.c

@@ -1514,7 +1514,9 @@ static int rx_rtp(struct msgb *msg)
 
 	LOG_CONN_RTP(conn_src, LOGL_DEBUG, "rx_rtp(%u bytes)\n", msgb_length(msg));
 
-	mgcp_conn_watchdog_kick(conn_src->conn);
+	/* Check if the origin of the RTP packet seems plausible */
+	if (!trunk->rtp_accept_all && check_rtp_origin(conn_src, from_addr))
+		return -1;
 
 	/* If AMR is configured for the ingress connection and conversion of the
 	 * framing mode (octet-aligned vs. bandwith-efficient) is explicitly
@@ -1534,9 +1536,7 @@ static int rx_rtp(struct msgb *msg)
 		}
 	}
 
-	/* Check if the origin of the RTP packet seems plausible */
-	if (!trunk->rtp_accept_all && check_rtp_origin(conn_src, from_addr))
-		return -1;
+	mgcp_conn_watchdog_kick(conn_src->conn);
 
 	/* Execute endpoint specific implementation that handles the
 	 * dispatching of the RTP data */