iwlwifi: fix hidden ssid discovery in passive channels

This enables sending of direct probes on passive channels, as long as
traffic was detected on that channel. This enables connectivity to
hidden/non broadcasting SSIDs APs on passive channels. Note 5000 HW
declares all 5.2 spectrum as passive.

Signed-off-by: Cahill Ben <ben.m.cahill@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>