Bluetooth: Fix stand-alone HCI command handling

To have a consistent content for hdev->cmd_q all entries need to follow
the semantics of asynchronous HCI requests. This means that even single
commands need to be dressed as requests by having a request start
indicator. This patch adds these indicators to the two places needing
it (hci_send_cmd and hci_sock_sendmsg).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>