can: add missing attribute validation for termination

Add missing attribute validation for IFLA_CAN_TERMINATION
to the netlink policy.

Fixes: 12a6075c ("can: dev: add CAN interface termination API")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>