iwlwifi: dvm: don't send BT_CONFIG on devices w/o Bluetooth

The BT_CONFIG command that is sent to the device during
startup will enable BT coex unless the module parameter
turns it off, but on devices without Bluetooth this may
cause problems, as reported in Redhat BZ 885407.

Fix this by sending the BT_CONFIG command only when the
device has Bluetooth.

Cc: stable@vger.kernel.org
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>