kdbus.h: rename KDBUS_{ITEM,ATTACH}_CONN_NAME → KDBUS_{ITEM,ATTACH}_CONN_DESCRIPTION

To not overload the term 'name' too much, rename the attach flag and
the item type to 'DESCRIPTION'.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Add Changelog as template for next cover letter

Signed-off-by: Daniel Mack <daniel@zonque.org>