iwl4965: exclude 60M rate from probe request

This patch do the following 2 things:
1. Make sure we don't add rate 60M part of supported rate in proble request,
   some AP does not like that.
2. It is wrong to set priv->active_rate in this function, this will set
   it to all avialable rates which might overwrite the mode supported rate.
   priv->active_rate should be set by only from iwl_set_rate.

Signed-off-by: Mohamed Abbas <mabbas@linux.intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>