Bug#33302441 mock-server warns about tls::zero_return

Problem
=======

When closing a connection to the mysql_server_mock its error-log
contains:

  tls::zero_return

which is return by openssl on connection-close.

Change
======

- map tls::zero_return to net::stream_errc::eof which does the same
  and is properly suppressed.

RB: 26936

Author: weigon

router/src/mock_server/src/statement_reader.h

@@ -171,6 +171,11 @@ class ProtocolBase {
     }
   }
 
+  // TlsErrc to net::stream_errc if needed.
+  static std::error_code map_tls_error_code(std::error_code ec) {
+    return (ec == TlsErrc::kZeroReturn) ? net::stream_errc::eof : ec;
+  }
+
   template <class CompletionToken>
   void async_receive_tls(CompletionToken &&token) {
     net::async_completion<CompletionToken, void(std::error_code, size_t)> init{
@@ -208,9 +213,11 @@ class ProtocolBase {
       } else {
         // as we can't handle the error, forward the error to the
         // completion handler
-        net::defer(client_socket_.get_executor(),
-                   [compl_handler = std::move(init.completion_handler),
-                    ec = read_ec]() { compl_handler(ec, {}); });
+
+        net::defer(
+            client_socket_.get_executor(),
+            [compl_handler = std::move(init.completion_handler),
+             ec = map_tls_error_code(read_ec)]() { compl_handler(ec, {}); });
       }
     } else {
       // success, forward it to the completion handler