mgcp: Allocate a different port for the networking...

Use the right source port when sending the message.
diff --git a/openbsc/src/mgcp/mgcp_protocol.c b/openbsc/src/mgcp/mgcp_protocol.c
index 8dbe2b0..211ec3e 100644
--- a/openbsc/src/mgcp/mgcp_protocol.c
+++ b/openbsc/src/mgcp/mgcp_protocol.c
@@ -429,6 +429,8 @@
 	/* bind to the port now */
 	port = rtp_calculate_port(ENDPOINT_NUMBER(endp), cfg->rtp_bts_base_port);
 	endp->bts_end.local_port = port;
+
+	port = rtp_calculate_port(ENDPOINT_NUMBER(endp), cfg->rtp_net_base_port);
 	endp->net_end.local_port = port;
 
 	/* assign a local call identifier or fail */
@@ -709,6 +711,7 @@
 	cfg->audio_name = talloc_strdup(cfg, "GSM-EFR/8000");
 	cfg->audio_payload = 97;
 	cfg->rtp_bts_base_port = RTP_PORT_DEFAULT;
+	cfg->rtp_net_base_port = RTP_PORT_NET_DEFAULT;
 
 	return cfg;
 }