sd-bus: sync kdbus.h (ABI break)

Catch up with some changes in kdbus.h:

  * KDBUS_{ITEM,ATTACH}_CONN_NAME were renamed to
    KDBUS_{ITEM,ATTACH}_CONN_DESCRIPTION, so the term 'name' is not
    overloaded as much.

  * The item types were re-ordered a little so they are lined up to the
    order of the corresponding KDBUS_ATTACH flags

  * A new item type KDBUS_ITEM_OWNED_NAME was introduced, designated to
    store a struct kdbus_name in item->name. KDBUS_ITEM_NAME soley
    stores data in item->str now

  * Some kerneldoc fixes