osmux: Allow to listen to a specific address

For a setup with multiple network interfaces be able to pick
the one that osmux should be used/visible.
diff --git a/openbsc/src/libmgcp/mgcp_osmux.c b/openbsc/src/libmgcp/mgcp_osmux.c
index 2d39b2c..be0db99 100644
--- a/openbsc/src/libmgcp/mgcp_osmux.c
+++ b/openbsc/src/libmgcp/mgcp_osmux.c
@@ -415,7 +415,7 @@
 	}
 	osmux_fd.data = cfg;
 
-	ret = mgcp_create_bind("0.0.0.0", &osmux_fd, cfg->osmux_port);
+	ret = mgcp_create_bind(cfg->osmux_addr, &osmux_fd, cfg->osmux_port);
 	if (ret < 0) {
 		LOGP(DMGCP, LOGL_ERROR, "cannot bind OSMUX socket\n");
 		return ret;