network: ignore stale interface renames

network: ignore stale interface renames

After enumeration, networkd may receive RTM_NEWLINK messages carrying a
stale interface name. This can happen when interface rename notifications
are queued before link enumeration and processed afterwards.

Previously, networkd could become confused by such a message and put the
corresponding Link into the failed state. Avoid this by checking whether
the new interface name is already in use by another interface and ignoring
the rename if so.

Fixes #20203.