Bluetooth: Connection Parameter Update Procedure

This patch adds support for LE Connection Parameters Request Link
Layer control procedure introduced in Core spec 4.1. This procedure
allows a Peripheral or Central to update the Link Layer connection
parameters of an established connection.

Regarding the acceptance of connection parameters, the LL procedure
follows the same approach of L2CAP procedure (see l2cap_conn_param_
update_req function). We accept any connection parameters values as
long as they are within the valid range.

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