Fix DNS port typo in RSS

[jgallagher]

I'm still waiting for a4x2 to come all the way up to confirm Nexus can update internal DNS, but based on the serialized RSS plan, I believe this should be all that's required; the port numbers are correct with this change:

          "_nameservice._tcp": [
            {
              "type": "SRV",
              "data": {
                "prio": 0,
                "weight": 0,
                "port": 5353,
                "target": "9340319c-02e3-4bed-9a58-761e6dba81c4.host.control-plane.oxide.internal"
              }
            },
            {
              "type": "SRV",
              "data": {
                "prio": 0,
                "weight": 0,
                "port": 5353,
                "target": "dc93338b-b6f2-42c6-b70d-ae4b62d04c90.host.control-plane.oxide.internal"
              }
            },
            {
              "type": "SRV",
              "data": {
                "prio": 0,
                "weight": 0,
                "port": 5353,
                "target": "dd8536a6-9736-4a84-bee8-43db57303f12.host.control-plane.oxide.internal"
              }
            }

Fixes #6951.

[andrewjstone]

Thanks @jgallagher!