Bluetooth: Introduce connection parameters list

This patch adds to hdev the connection parameters list (hdev->
conn_param). The elements from this list (struct hci_conn_param)
contains the connection parameters (for now, minimum and maximum
connection interval) that should be used for establishing
connection.

The struct hci_conn_param also defines the 'auto_connect' field
which will be used to implement the auto connection mechanism.

This patch also adds helper functions to manipulate hdev->conn_
param list. Some of these function 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>