Bluetooth: Controller: Fix missing ext adv terminate event

Fix missing Extended Advertising terminate event and
advertising scheduling not being stopped.

Under race conditions, auxiliary event is aborted without
the generation  of done extra event which is suppose to
stop the scheduling when max events count is used.

The fix now generates the done extra event.

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