Removed "callback failed" error message from tls_inspector.cc

The TLS inspector listener filter installs a servername callback (using
SSL_CTX_set_tlsext_servername_callback()). That callback obtains the server
name and then halts the handshake by returning SSL_TLSEXT_ERR_ALERT_FATAL.
It does this because once it has obtained the server name, it has no need
to progress the handshake any further because it's only "peeking" at the
received data, and not actually doing the "real" handshake. In upstream
envoy, on BoringSSL, this is OK, but on OpenSSL the SSL_TLSEXT_ERR_ALERT_FATAL
return value causes a "callback failed" error message to be logged. It turns
out this error message is innocuous, but it is unsigtly and distracting, so
this commit removes it by returning SSL_TLSEXT_ERR_OK instead.

Signed-off-by: Ted Poole <[email protected]>

source/extensions/filters/listener/tls_inspector/tls_inspector.cc

@@ -89,7 +89,7 @@ Config::Config(
 
         // Return an error to stop the handshake; we have what we wanted already.
         *out_alert = SSL_AD_USER_CANCELLED;
-        return SSL_TLSEXT_ERR_ALERT_FATAL;
+        return SSL_TLSEXT_ERR_OK;
       });
 }