Bluetooth: Controller: Fix hang due to loop in node_rx list

Fix Controller hang due to infinite looping caused by
duplicate node_rx enqueued in auxiliary context.

When LLL scheduling is not applied due to invalid aux offset
then ULL scheduling too would skip setting up the reception
after similarly checking the validity of aux offset required
to schedule the reception of auxiliary PDU. This check in
ULL was after the received node_rx being enqueued into the
auxiliary context causing a loop in the list of node_rx.

Dequeue of a list with a loop of node_rx caused an infinite
loop execution in the Controller.

Regression introduced in commit 3590bd64 ("Bluetooth:
Controller: Fix missing invalid aux offset check").

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