Bluetooth: Controller: Fix auxiliary scan context leak

Fix an auxiliary scan context leak when initiator
establishes a connection while there is another pending
auxliary PDU scheduled to be received. In this case, the
pending auxliary scan LLL context does an early abort
without generating a scan aux done event. Missing scan aux
done event caused the auxiliary scan context leak.

Fixes #36131.

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