MINOR: proto_uxst: add resume method

resume method was not explicitly defined for uxst protocol family.
Here we can safely use the default_resume_listener, just like the uxdg family.

This could be backported up to 2.4.
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index fd22e95..08b8d27 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -57,6 +57,7 @@
 	.add            = default_add_listener,
 	.unbind         = default_unbind_listener,
 	.suspend        = default_suspend_listener,
+	.resume         = default_resume_listener,
 	.accept_conn    = sock_accept_conn,
 	.ctrl_init      = sock_conn_ctrl_init,
 	.ctrl_close     = sock_conn_ctrl_close,