Expand network error callback

ortp: use extra parameter for network_error callback in log message as
it's described in oRTP documentation (error string).

Change-Id: I581db499d453b80230198d95000f0f6fc20752d1
diff --git a/src/trau/osmo_ortp.c b/src/trau/osmo_ortp.c
index f7adc93..0f0b9e5 100644
--- a/src/trau/osmo_ortp.c
+++ b/src/trau/osmo_ortp.c
@@ -130,7 +130,7 @@
 	int port = rtp_session_get_local_port(rs);
 
 	LOGP(DLMIB, LOGL_ERROR,
-	     "osmo-ortp(%d): network_error\n", port);
+	     "osmo-ortp(%d): network_error %s\n", port, (char *)data);
 }
 
 static void ortp_sig_cb_ts(RtpSession *rs, void *data)