udev/net: assign alternative names only on add uevent

udev/net: assign alternative names only on add uevent

Previously, we first assign alternative names to a network interface,
then later change its main name if requested. So, we could not assign
the name that currently assigned as the main name of an interface as an
alternative name. So, we retry to assign the previous main name as an
alternative name on later move uevent.

However, that causes some confusing situation. E.g. if a .link file has
```
Name=foo
AlternativeNames=foo baz
```
then even if the interface is renamed by a user e.g. by invoking 'ip link'
command manually, the interface can be still referenced as 'foo', as the
name is now assigned as an alternative name.

This makes the order of name assignment inverse: the main name is first
changed, and then the requested alternative names are assigned. And
udevd do not assign alternative names on move uevent.

Replaces #27506.