[resolve] TCP errors are flagged as TLS errors

When running blaeau-resolve --tcp, purely TCP errors such as "connection refused" are displayed as TLS errors. For instance, in measurement #15279208, we have:

    "error": {
      "TUCONNECT": "Connection refused"
    },

But Blaeu displays:

% blaeu-resolve --measurement-ID 15279169   gitlab.isc.org 
[TUCONNECT (may be a TLS negotiation error)] : 12 occurrences