Fix IuUP RTP hdr seqnr field not incremented

Previous commit add osmo_io changed mgcp_udp_send() implementation from
"return sendto()", which is documented as:
"return the number of bytes sent. Otherwise, -1 shall be returned"

to "return mgcp_udp_send_msg()", which in turn calls
"return osmo_iofd_sendto_msgb()", and which is documented as:
"\returns 0 in case of success (takes msgb ownership), -1 on error
(doesn't take msgb ownership)."

So successful return code changed from >0 (bytes sent) to ==0,
but forgot to update mgcp_send_iuup() return code path check (and also
some related function documentation calling mgcp_udp_send()".

This commit fixes all the related aspects of that return code change.

Related: SYS#6907
Fixes: 352b967d1bee4b3bc51ecc383306bad0fc5b7fbf
Change-Id: I154e1e41cd02fd4d9b88ad98fc7c4d657246c589
---
M src/libosmo-mgcp/mgcp_iuup.c
M src/libosmo-mgcp/mgcp_network.c
M src/libosmo-mgcp/mgcp_osmux.c
3 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/src/libosmo-mgcp/mgcp_iuup.c b/src/libosmo-mgcp/mgcp_iuup.c
index 7531e42..d6f164d 100644
--- a/src/libosmo-mgcp/mgcp_iuup.c
+++ b/src/libosmo-mgcp/mgcp_iuup.c
@@ -468,7 +468,7 @@
 	struct rtp_hdr *hdr = (struct rtp_hdr *)msgb_data(msg);
 	int buflen = msgb_length(msg);
 	char *dest_name;
-	int len;
+	int rc;
 
 	OSMO_ASSERT(conn_src);
 	OSMO_ASSERT(conn_dst);
@@ -514,16 +514,16 @@
 	/* Forward a copy of the RTP data to a debug ip/port */
 	forward_data_tap(rtp_end->rtp, &conn_src->tap_out, msg);
 
-	len = mgcp_udp_send(rtp_end->rtp, &rtp_end->addr, (char *)hdr, buflen);
+	rc = mgcp_udp_send(rtp_end->rtp, &rtp_end->addr, (char *)hdr, buflen);
 
-	if (len <= 0)
-		return len;
+	if (rc < 0)
+		return rc;
 
 	rtpconn_rate_ctr_add(conn_dst, endp, RTP_PACKETS_TX_CTR, 1);
-	rtpconn_rate_ctr_add(conn_dst, endp, RTP_OCTETS_TX_CTR, len);
+	rtpconn_rate_ctr_add(conn_dst, endp, RTP_OCTETS_TX_CTR, buflen);
 	rtp_state->alt_rtp_tx_sequence++;
 
-	return len;
+	return 0;
 }
 
 /* Received TNL primitive from IuUP layer FSM, transmit it further down to the
diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index 1fc2c56..58d85df 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -1062,7 +1062,7 @@
  *  \param[in] addr destination ip-address.
  *  \param[in] buf buffer that holds the data to be send.
  *  \param[in] len length of the data to be sent.
- *  \returns bytes sent, -1 on error. */
+ *  \returns 0 in case of success, -1 on error. */
 int mgcp_udp_send(struct osmo_io_fd *iofd, const struct osmo_sockaddr *addr, const char *buf, int len)
 {
 	struct msgb *msg = msgb_alloc_c(iofd, len, "mgcp_udp_send");
@@ -1077,7 +1077,7 @@
 /*! send RTP dummy packet (to keep NAT connection open).
  *  \param[in] endp mcgp endpoint that holds the RTP connection.
  *  \param[in] conn associated RTP connection.
- *  \returns bytes sent, -1 on error. */
+ *  \returns 0 in case of success, -1 on error. */
 int mgcp_send_dummy(struct mgcp_endpoint *endp, struct mgcp_conn_rtp *conn)
 {
 	int rc;
@@ -1113,7 +1113,7 @@
 	rc = mgcp_udp_send(conn->end.rtcp, &rtcp_addr,
 			   rtp_dummy_payload, sizeof(rtp_dummy_payload));
 
-	if (rc >= 0)
+	if (rc == 0)
 		return rc;
 
 failed:
diff --git a/src/libosmo-mgcp/mgcp_osmux.c b/src/libosmo-mgcp/mgcp_osmux.c
index df91dbc..f8383d6 100644
--- a/src/libosmo-mgcp/mgcp_osmux.c
+++ b/src/libosmo-mgcp/mgcp_osmux.c
@@ -695,7 +695,7 @@
 
 /*! send RTP dummy packet to OSMUX connection port.
  *  \param[in] conn associated RTP connection
- *  \returns bytes sent, -1 on error */
+ *  \returns 0 in case of success, -1 on error */
 int osmux_send_dummy(struct mgcp_conn_rtp *conn)
 {
 	char ipbuf[INET6_ADDRSTRLEN];

