- Add all existing mdio(4) clients (and dependencies) to
the kernel config (note that this excludes if_mge (ARM-specific) and e6000sw (not built in current tree):
```
device etherswitch
device arswitch
device ip17x
device rtl8366rb
device ukswitch
device miiproxy
device iicbus
```
- Verify that the kernel still builds.