Bluetooth: Fix updating advertising data needlessly

We need to ensure that the advertising data is up-to-date whenever
advertising is enabled, but when disabling advertising we do not need to
worry about it (since it will eventually get fixed as soon as
advertising is enabled again). This patch fixes this in the command
complete callback for set_adv_enable.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>