iwlagn: keep BT settings across restart

The BT SCO needs to be re-applied to the device,
while the traffic load just needs to be correct
in software.

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>