Update 6201 doesn't rename all menu-related variables correctly, due to a bug in xmlsitemap_link_type_rename()

When running update 6201 to change the 'menu' entity name to 'menu link', there is a problem with some of the variable updates.

Any menu that has the word "menu" in its name will have its associated variable renamed incorrectly, so its XML Sitemap settings won't be preserved after the upgrade. For example, the variable 'xmlsitemap_settings_menu_main-menu' gets renamed to 'xmlsitemap_settings_menu_link_main-menu_link', but it actually should be 'xmlsitemap_settings_menu_link_main-menu'.

This is due to a more general bug in xmlsitemap_link_type_rename(). The attached patch is a simple fix.