mgcp: Allow to omit sending the audio name at all

Equipment like AudioCode appears to get upset when we use a
builtin type and then assign a name to it. Allow to completely
omit the name.
diff --git a/openbsc/src/libmgcp/mgcp_protocol.c b/openbsc/src/libmgcp/mgcp_protocol.c
index 79422fe..98452ce 100644
--- a/openbsc/src/libmgcp/mgcp_protocol.c
+++ b/openbsc/src/libmgcp/mgcp_protocol.c
@@ -274,7 +274,7 @@
 
 		len += nchars;
 
-		if (audio_name) {
+		if (audio_name && endp->tcfg->audio_send_name) {
 			nchars = snprintf(sdp_record + len, size - len,
 					  "a=rtpmap:%d %s\r\n",
 					  payload_type, audio_name);
@@ -1417,6 +1417,7 @@
 	cfg->trunk.audio_name = talloc_strdup(cfg, "AMR/8000");
 	cfg->trunk.audio_payload = 126;
 	cfg->trunk.audio_send_ptime = 1;
+	cfg->trunk.audio_send_name = 1;
 	cfg->trunk.omit_rtcp = 0;
 	mgcp_trunk_set_keepalive(&cfg->trunk, MGCP_KEEPALIVE_ONCE);
 
@@ -1441,6 +1442,7 @@
 	trunk->audio_name = talloc_strdup(cfg, "AMR/8000");
 	trunk->audio_payload = 126;
 	trunk->audio_send_ptime = 1;
+	trunk->audio_send_name = 1;
 	trunk->number_endpoints = 33;
 	trunk->omit_rtcp = 0;
 	mgcp_trunk_set_keepalive(trunk, MGCP_KEEPALIVE_ONCE);