Bluetooth: Introduce connection parameters list

Bluetooth: Introduce connection parameters list

This patch adds to hdev the connection parameters list (hdev->le_
conn_params). The elements from this list (struct hci_conn_params)
contains the connection parameters (for now, minimum and maximum
connection interval) that should be used during the connection
establishment.

Moreover, this patch adds helper functions to manipulate hdev->le_
conn_params list. Some of these functions are also declared in
hci_core.h since they will be used outside hci_core.c in upcoming
patches.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>