Bluetooth: Controller: lll: df: Check CTEPRESENT before radio reset

The radio_df_cte_ready function returns state of EVENTS_CTEPRESENT.
The function may not be used in create_iq_report function, because
it is called after lll_isr_rx_status_reset. The lll_isr_rx_status-
_reset clears EVENTS_CTEPRESENT value.

The result of this calls chain is lack of IQ sample report no matter
if the PDU has CTEInfo and radio has collected IQ samples.

To fix the problem, state of EVENTS_CTEPRESENT has to be get when
e.g. rssi_ready is get.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>