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_stat.c b/src/libosmo-mgcp/mgcp_stat.c
index acc9419..c66ce6b 100644
--- a/src/libosmo-mgcp/mgcp_stat.c
+++ b/src/libosmo-mgcp/mgcp_stat.c
@@ -99,7 +99,7 @@
 	str += nchars;
 	str_len -= nchars;
 
-	if (conn->conn->endp->trunk->cfg->osmux_use != OSMUX_USAGE_OFF) {
+	if (conn->conn->endp->trunk->cfg->osmux.usage != OSMUX_USAGE_OFF) {
 		/* Error Counter */
 		nchars = snprintf(str, str_len,
 				  "\r\nX-Osmo-CP: EC TI=%" PRIu64 ", TO=%" PRIu64,