osmux: Clean up mgcp_config osmux fields

* Move all of them to an anonymous "osmux" substruct to have them all
  together.
* Rename some fields to clarify its meanings, similar to what
  was already done in osmo-bts.
* Move the port VTY config next to the ip address ones.

Change-Id: Icc1c1ce3ab3a8beb941cda7c112485a0db882a90
diff --git a/src/libosmo-mgcp/mgcp_sdp.c b/src/libosmo-mgcp/mgcp_sdp.c
index 1414cf9..ad2da7f 100644
--- a/src/libosmo-mgcp/mgcp_sdp.c
+++ b/src/libosmo-mgcp/mgcp_sdp.c
@@ -601,7 +601,7 @@
 
 		payload_types[0] = payload_type;
 		if (mgcp_conn_rtp_is_osmux(conn))
-			local_port = endp->trunk->cfg->osmux_port;
+			local_port = endp->trunk->cfg->osmux.local_port;
 		else
 			local_port = conn->end.local_port;
 		rc = add_audio(sdp, payload_types, 1, local_port);