Fix false LLDP_MISMATCH: compare the switch's name with the server's lldpd neighbour

The switch port's LLDP entry describes the server, while the server's lldpctl
describes the switch, so the two were never comparable and every link with lldpd
running was flagged as cross-cabled. Pass the switch name in the port data and
compare it with the server's neighbour instead; skip the check without it.

app.py

@@ -436,6 +436,7 @@ def api_diagnose_start():
         if pd.get('port_idx') == port_idx:
             port_data = dict(pd)
             port_data['name'] = pname
+            port_data['switch_name'] = switch_name
             break
     if not port_data:
         return jsonify({'error': f'Port {port_idx} not found on switch "{switch_name}"'}), 404