team: account for oper state

Account for operational state when determining port linkup state,
as per Documentation/networking/operstates.txt.

Signed-off-by: George Wilkie <gwilkie@vyatta.att-mail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>