core: document CleanupType

We must do different cleanups depending on the CleanupType. Document the
meaning of the different types as it was very confusing to work on new
code without having very clear what do they mean.

src/core/devices/nm-device.c

@@ -113,6 +113,19 @@ typedef enum {
     RELEASE_PORT_TYPE_CONFIG_FORCE,
 } ReleasePortType;
 
+/**
+ * CleanupType:
+ * @CLEANUP_TYPE_KEEP: Cleanup internally but keep the real device's config. This is
+ *   often used when moving a partially managed device to "unmanaged" (but not only).
+ * @CLEANUP_TYPE_REMOVED: The device suddently disappeared. Cleanup internally but don't
+ *   make any action on the real device at all, as it no longer exists.
+ * @CLEANUP_TYPE_DECONFIGURE: Also deconfigure the real device. This is the typical
+ *   action when a connection or device is set to "down", or fully managed devices
+ *   moved to "unmanaged".
+ * @CLEANUP_TYPE_KEEP_REAPPLY: Like %CLEANUP_TYPE_KEEP, but indicating that it's a
+ *   reapply. Some special actions can be done if we're doing a reapply, like keeping
+ *   the existing DHCP lease, for example.
+ */
 typedef enum {
     CLEANUP_TYPE_KEEP,
     CLEANUP_TYPE_REMOVED,