Creates a link from this to model if non-null, or unsets
it.
Links are used to establish a relationship between a particular menu item and another menu. For example, g_menu_link_submenu is used to associate a submenu with a particular menu item, and g_menu_link_section is used to create a section. Other types of link can be used, but there is no guarantee that clients will be able to make sense of them. Link types are restricted to lowercase characters, numbers and '-'. Furthermore, the names must begin with a lowercase character, must not end with a '-', and must not contain consecutive dashes.
| this |
a MenuItem |
| link |
type of link to establish or unset |
| model |
the MenuModel to link to (or null to unset) |