IB/rxe: Handle NETDEV_CHANGE events

Without this fix, ports configured on top of ixgbe miss link up
notifications. ibv_query_port() will continue to return IBV_PORT_DOWN even
though the port is up and working.

Fixes: 8700e3e7 ("Soft RoCE driver")
Signed-off-by: Andrew Boyer <andrew.boyer@dell.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>