Intel i226 doesn't work correctly on 2.5 Gbps networks

As documented in #2, the i226 NIC on the TimeHAT doesn't seem to get any network connection when I plug it into a 2.5 Gbps network switch. If I manually **force** the 1 Gbps link speed, it starts working:

```
ethtool -s eth1 autoneg on speed 1000 duplex full
```

Also, currently I have to manually force an IPv4 address as DHCP seems to not be working, and since I'm not testing IPv6, I've also [disabled IPv6](https://itslinuxfoss.com/disable-ipv6-debian-12/). This might get fixed if I update the firmware for the i226... maybe.

If I plug it into a 1 Gbps switch, it works fine too.

It'd be nice to get 2.5 Gbps speeds, though. So far none of the tricks I've found online seem to work.