mac80211: Fix scan_ies_len to include DS Params

Commit 651b5225 added DS Parameter Set
information into Probe Request frames that are transmitted on 2.4 GHz
band, but it failed to increment local->scan_ies_len to cover this new
information. This variable needs to be updated to match the maximum IE
data length so that the extra buffer need gets reduced from the driver
limit.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>