Fix eradius_client after the dialyzer checks
Fix eradius_client after the dialyzer checks

* Fix spec for `send_request/3`.
In success it alway returns `{ok, binary(), eradius_lib:authenticator()}`.

* Remove `proceed_response(Request, Value, Peer, TS1, undefined)`.
Because `MetricsInfo` can't be `undefined`.

* Use `null` as possible type for socket_ip.
Because `null` is incorrect value for `inet:ip_address()`

surik/eradius