wl1271: fixed problem with WPS IEs in probe requests

Inclusion of a WPS IE in probe requests caused a problem
in the driver due to the maximum size of the probe request
template and the max_scan_ie_len values at initialization.

Increased the size of probe request template
to the maximum size allowed by the firmware.
Struct wl12xx_probe_req_template, which was only used
for calculating the max size of the probe request template,
is no longer used and needed.

max_scan_ie_len is used for validating the size of
additional IEs in scan requests.
Initialized the max_scan_ie_len field to the maximum size
of the probe request template minus the ieee80211 header size.

Signed-off-by: Guy Eilam <guy@wizery.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>