MXS-2763: Log correct error for unsupported TLS versions

Previously when ssl_version was used with a value that is not supported on
the system, an unknown parameter error was returned. This could be
confusing and logging a proper error message should make it clear.

server/core/config.cc

@@ -279,13 +279,9 @@ static const MXS_ENUM_VALUE ssl_values[] =
 static const MXS_ENUM_VALUE ssl_version_values[] =
 {
     {"MAX",    SERVICE_SSL_TLS_MAX},
-#ifndef OPENSSL_1_1
     {"TLSv10", SERVICE_TLS10      },
-#endif
-#ifdef OPENSSL_1_0
     {"TLSv11", SERVICE_TLS11      },
     {"TLSv12", SERVICE_TLS12      },
-#endif
     {NULL}
 };