add ctrl_interface_setup_dynip() for bind address

Make the ctrl interface bind address configurable, so that it may be made
available on other addresses than 127.0.0.1. The specific aim is to allow
running multiple osmo-nitbs alongside each other (commits in openbsc follow).
diff --git a/src/ctrl/control_if.c b/src/ctrl/control_if.c
index 18e695d..bde245d 100644
--- a/src/ctrl/control_if.c
+++ b/src/ctrl/control_if.c
@@ -673,6 +673,14 @@
 struct ctrl_handle *ctrl_interface_setup(void *data, uint16_t port,
 					 ctrl_cmd_lookup lookup)
 {
+	return ctrl_interface_setup_dynip(data, "127.0.0.1", port, lookup);
+}
+
+struct ctrl_handle *ctrl_interface_setup_dynip(void *data,
+					       const char *bind_addr,
+					       uint16_t port,
+					       ctrl_cmd_lookup lookup)
+{
 	int ret;
 	struct ctrl_handle *ctrl;
 
@@ -693,7 +701,7 @@
 	ctrl->listen_fd.cb = listen_fd_cb;
 	ctrl->listen_fd.data = ctrl;
 	ret = osmo_sock_init_ofd(&ctrl->listen_fd, AF_INET, SOCK_STREAM, IPPROTO_TCP,
-				 "127.0.0.1", port, OSMO_SOCK_F_BIND);
+				 bind_addr, port, OSMO_SOCK_F_BIND);
 	if (ret < 0)
 		goto err_vec;