hw/net/can: Make CanBusClientInfo::can_receive() return a boolean

hw/net/can: Make CanBusClientInfo::can_receive() return a boolean

The CanBusClientInfo::can_receive handler return whether the
device can or can not receive new frames. Make it obvious by
returning a boolean type.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>