Bluetooth: Controller: Fix extended scanning data length assertion

Fix assertion due to LLL scheduling of auxiliary PDU
reception was not considered in the ULL when checking for
accumulated data length exceeding the supported maximum scan
data length. This caused the auxiliary context to be release
while LLL was still active with scheduled PDU reception.

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