nl80211/cfg80211: add max_sched_scan_ie_len in the hw description

Some chips may support different lengths of user-supplied IEs with a
single scheduled scan command than with a single normal scan command.

To support this, this patch creates a separate hardware description
element that describes the maximum size of user-supplied information
element data supported in scheduled scans.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>