iwlagn: set BT IGNORE for some frames

The BT ignore bit should be set when transmitting
auth, assoc response and eap frames.

Also, scanning should set the BT ignore bit for the
probe request transmission; Note that we only use
the non-shared antenna.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>