[infiniband] Reset port state after closing device

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/infiniband.c

 		ib_destroy_sma ( ibdev, ibdev->smi );
 		ib_destroy_mi ( ibdev, ibdev->smi );
 		ibdev->op->close ( ibdev );
+		ibdev->port_state = IB_PORT_STATE_DOWN;
 	}
 }