Add passive_scan configuration parameter

Add passive_scan configuration parameter

This new wpa_supplicant configuration parameter can be used to force
passive scanning to be used for most scanning cases at the cost of
increased latency and less reliably scans. This may be of use for both
testing purposes and somewhat increased privacy due to no Probe Request
frames with fixed MAC address being sent out.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>