Expose firmware limit for the max_scan_ie_len;
also do actually set IE's for the probe request

max_scan_ie_len used to be 0, this blocks scan requests with non-zero IE's
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>