iwl3945 : Fix a-band association for passive channels

Patch does following things
    1) This patch fixes the a-band association for passive channels with new
    uCode feature that it allows direct scan on passive channels after
    auto-switch from passive to active. This enables sending of direct probes
    on passive channels, as long as some traffic is detected on that channel.
    This improves the scanning for hidden SSIDs in A-band,which is all
    passive channels.

    This patch fixes the bug no 1748.

        http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1748



    2) This fix will only work with uCode version 15.28.2.8 and above.
    Prior versions of uCode would work only if we heard the traffic within
     active dwell time, which is much shorter than passive dwell time and
    is shorter than typical beacon periods. This patch also provids full
    active dwell time even if we hear traffic late in passive dwell.

    3) uCode API version is incremented to 2.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Acked-by: Ben Cahill <ben.m.cahill@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>