Bluetooth: controller: Fix connection terminate to happen on event done

Fix conn_cleanup to be performed in the event done. The
regression was introduced in
commit 5412f61a ("Bluetooth: controller: Introduce
separate done memq").

Now that done event is handled asynchronously outside the
handling of the terminate node rx type, it is necessary that
terminate node rx type is generated after the done event.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>