team: add missing attribute validation for port ifindex

Add missing attribute validation for TEAM_ATTR_OPTION_PORT_IFINDEX
to the netlink policy.

Fixes: 80f7c668 ("team: add support for per-port options")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>