Bluetooth: Controller: Make node rx release code conditionally reusable

Make the block of code that is used to release node rx with
type NODE_RX_TYPE_RELEASE to be conditionally available for
other Kconfig selectable features like Extended Scanning.

Previously it was only available for CONFIG_BT_CONN, but now
Extended Scanning with LLL scheduling releases node rx when
radio event is closed due to failure to receive an auxiliary
PDU.

Relates to commit 2feffaf7 ("Bluetooth: Controller:
Release LLL scheduling aux on incomplete data").

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