Bluetooth: Change hci_conn_params_add to return the parameter struct

When adding new connection parameters, it is useful to return either
the existing struct or the newly created one.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

diff --cc include/net/bluetooth/hci_core.h
Simple merge

diff --cc net/bluetooth/hci_core.c
Simple merge