iwlwifi: rename PROBE_OPTION_MAX_API1 to PROBE_OPTION_MAX_3945

This limit applies to current (APIv1 and APIv2) 3945 firmware only, not
supported firmware of any of the other cards.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>