Bluetooth: Controller: Fix extended scanning for BT_CTLR_LOW_LAT

Fix Extended Scanning support for BT_CTLR_LOW_LAT variant
of the Controller implementation by closing the scan window
for every ADV_EXT_IND PDU received that that ULL_LOW context
is enabled back and ticker job can process the request to
start auxiliary PDU reception. Without the change the
ticker job would only run at the end of the scan window that
caused the auxiliary scan prepare to assert due to delayed
ticker timeout expiry callback.

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