migration/multifd: Make MultiFDMethods const

The methods are defined at module_init time and don't ever
change. Make them const.

Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
7 files changed