osmo_ortp: Don't print ERROR message for every missing RTP frame

* it's inconsistent to print ERROR in a LOGL_INFO message
* loosing RTP packets is not that unusual, especially when the channel
  is just starting up

Change-Id: Ide0017987b4cea7fd24795941494f1da913ea673
Closes: OS#4464
diff --git a/src/trau/osmo_ortp.c b/src/trau/osmo_ortp.c
index 0cd4e9d..6e91f8d 100644
--- a/src/trau/osmo_ortp.c
+++ b/src/trau/osmo_ortp.c
@@ -202,8 +202,10 @@
 	if (recv_with_cb(rs))
 		return 1;
 
-	LOGP(DLMIB, LOGL_INFO, "osmo_rtp_socket_poll(%u): ERROR!\n",
-	     rs->rx_user_ts);
+	/* this happens every time we miss an incoming RTP frame, which is quite common
+	 * when a voice channel is first activated, or also in case of packet loss.
+	 * See also https://osmocom.org/issues/4464 */
+	LOGP(DLMIB, LOGL_DEBUG, "osmo_rtp_socket_poll(%u): No message received\n", rs->rx_user_ts);
 	return 0;
 }