In Nomad Enterprise we can fingerprint multiple Consul datacenters. If neither
is `"default"` then we end up with warning logs about adding a "link".
The `Link` field on the `Node` struct is a map of attributes that only
contributes to the node's computed hash. The `"consul"` key's value is derived
from the `unique.consul.name` attribute, which only exists if there's a default
Consul cluster.
Update the fingerprint to skip setting the link field if there's no
`unique.consul.name`, and lower the warning log for malformed fields to debug;
this is a minor scheduling optimization largely captured by existing Consul
fields in the node computed class. The only reason not to remove it entirely is
to avoid changing computed classes on existing large clusters.
Fixes: https://github.com/hashicorp/nomad/issues/26781
Ref: https://hashicorp.atlassian.net/browse/NMD-998
3432b0a2d6