network/netdev: replace old NetDev object with newer one on reload

network/netdev: replace old NetDev object with newer one on reload

Then, when a .netdev file of a stacked netdev is modified, the netdev
can be reconfigured with the updated setting by something like the
following way:
```
ip link del vlan99
networkctl reload
```

Note, removing the vlan interface in the above example may not be necessary,
e.g. when only VLAN flags, egress mapping, or ingress mapping are updated.
But, it is necessary when VLAN ID is updated.

Closes #9627.
Closes #27177.
Closes #34907.
Replaces #22557.