* Add remote_port in the audit logs when it is available

The `request.remote_port` field is now present in the audit log when it
is available:

```
{
  "time": "2021-10-10T13:53:51.760039Z",
  "type": "response",
  "auth": {
    "client_token": "hmac-sha256:1304aab0ac65747684e1b58248cc16715fa8f558f8d27e90fcbcb213220c0edf",
    "accessor": "hmac-sha256:f8cf0601dadd19aac84f205ded44c62898e3746a42108a51105a92ccc39baa43",
    "display_name": "root",
    "policies": [
      "root"
    ],
    "token_policies": [
      "root"
    ],
    "token_type": "service",
    "token_issue_time": "2021-10-10T15:53:44+02:00"
  },
  "request": {
    "id": "829c04a1-0352-2d9d-9bc9-00b928d33df5",
    "operation": "update",
    "mount_type": "system",
    "client_token": "hmac-sha256:1304aab0ac65747684e1b58248cc16715fa8f558f8d27e90fcbcb213220c0edf",
    "client_token_accessor": "hmac-sha256:f8cf0601dadd19aac84f205ded44c62898e3746a42108a511...