iwlwifi: reset BT when going down

When we turn off the device, reset BT
data so that we don't have outdated
information when we come up again.

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>