#6274 introduced minor memleak

legacy/trac#6274 (moved) introduced this code in src/or/config.c:

  if (options->ServerTransportPlugin && !server_mode(options)) {
    log_notice(LD_GENERAL, "Tor is not configured as a relay but you specified"
               " a ServerTransportPlugin line (%s). The ServerTransportPlugin "
               "line will be ignored.",
               esc_for_log(options->ServerTransportPlugin->value));
  }

This is wrong use of esc_for_log() and results in a memleak.