rx_rule.control registers not getting bitflipped

This is backwards:

```
In <50>: dev.emac.rx_rule[7].control.word
Out<50>: 0xa400010c

In <51>: dev.emac.rx_rule[7].control.enable
Out<51>: 0x0

In <52>: dev.emac.rx_rule[7].control.offset
Out<52>: 0xa4
```

c.f. 57785-PG105-R fig 17
