sd-netlink: do not swap old name and alternative name

sd-netlink: do not swap old name and alternative name

Commit 434a348380 ("netlink: do not fail when new interface name is
already used as an alternative name") added logic to set the old
interface name as an alternative name, but only when the new name is
currently an alternative name. This is not the desired outcome in most
cases, and the important part of this commit was to delete the new name
from the list of alternative names if necessary.