Bluetooth: Make handle of hci_conn be unique

The handle of new hci_conn is always HCI_CONN_HANDLE_MAX + 1 if
the handle of the first hci_conn entry in hci_dev->conn_hash->list
is not HCI_CONN_HANDLE_MAX + 1. Use ida to manage the allocation of
hci_conn->handle to make it be unique.

Fixes: 9f78191c

 ("Bluetooth: hci_conn: Always allocate unique handles")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>