Bluetooth: Introduce hdev->pending_auto_conn list

This patch introduces the hdev->pending_auto_conn list which holds
the device addresses the kernel should autonomously connect. It also
introduces some helper functions to manipulate the list.

The list and helper functions will be used by the next patch which
implements the LE auto connection infrastructure.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Introduce LE auto connection infrastructure

This patch introduces the LE auto connection infrasctructure.
This infrastructre will be used to implement the auto_connect
options from hci_conn_params.

The auto connection mechanism works as follows: When the first
device address is inserted into hdev->pending_auto_con list, we
start the background scanning. Once the target device is found
in range, the kernel creates the connection. If connection is
established successfully, the device address is removed from
hdev->pending_auto_conn list. Finally, when the last device
address is removed, the background scanning is stopped.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bleutooth: Add support for auto connect options

This patch adds support for the HCI_AUTO_CONN_ALWAYS and HCI_AUTO_
CONN_LINK_LOSS options from struct hci_conn_params.

The HCI_AUTO_CONN_ALWAYS option configures the kernel to always re-
establish the connection, no matter the reason the connection was
terminated. This feature is required by some LE profiles such as
HID over GATT, Health Termomether and Blood Pressure. These profiles
require the host autonomously connect to the device as soon as it
enters in connectable mode (start advertising) so the device is able
to delivery a notification or indication.

The BT_AUTO_CONN_LINK_LOSS option configures the kernel to re-
establish the connection in case the connection was terminated due
to a link loss. This feature is required by the majority of LE
profiles such as Proximity, Find Me, Cycling Speed and Cadence and
Time.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Temporarily stop background scanning on discovery

If the user send a mgmt start discovery command while the background
scanning is running, we should temporarily stop it. Once the discovery
finishes, we start the background scanning again.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Auto connection and power on

This patch implements a fixup required by auto connection mechanism
in order to work properly after a power on.

When hdev is closed (e.g. Mgmt power off command, RFKILL or controller
is reset), the ongoing active connections are silently dropped by the
by the controller (no Disconnection Complete Event is sent to host).
For that reason, the devices that require HCI_AUTO_CONN_ALWAYS are not
add to hdev->pending_auto_conn list and they won't re-connect. So to
fix this issue, after adapter is powered on, we should add all HCI_
AUTO_CONN_ALWAYS address to hdev->pending_auto_conn list.

This way, the auto connection mechanism works propely after a power
off and power on sequence as well as RFKILL block/unblock.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>