Bluetooth: Fix removing adv when processing cmd complete

If we remove one instance of adv using Set Extended Adv Enable, there
is a possibility of issue occurs when processing the Command Complete
event. Especially, the adv_info might not be found since we already
remove it in hci_req_clear_adv_instance() -> hci_remove_adv_instance().
If that's the case, we will mistakenly proceed to remove all adv
instances instead of just one single instance.

This patch fixes the issue by checking the content of the HCI command
instead of checking whether the adv_info is found.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>