Bluetooth: hci_sync: Refactor add Adv Monitor

Make use of hci_cmd_sync_queue for adding an advertisement monitor.

Signed-off-by: Manish Mandlik <mmandlik@google.com>
Reviewed-by: Miao-chen Chou <mcchou@google.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>