hostap: Skip RSSI retrieval for AP mode

RSSI is only applicable for STA mode, as for AP there are multiple
peers. This causes failure and unnecessary delay, so just skip the
retrieval.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>