RDMA/rxe: Distinguish between down links and disabled links

In ib_query_port(), use the netdev's IFF_UP flag to determine phys_state
(flag set = down = POLLING, flag clear = disabled = DISABLED).

Callers can then use the phys_state field to distinguish between links
which have a dead partner, cable missing, etc., from links which are
turned off on the local node. This is useful for HA and supportability.

Signed-off-by: Andrew Boyer <andrew.boyer@dell.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>