config: Fix duplicate error message for nonlocal SocksPorts.

If `validate_only` is true, then just validate the configuration without warning
about it.  This way, we only emit warnings when the listener is actually opened.
(Otherwise, every time we parse the config we will might re-warn and we would
need to keep state; whereas the listeners are only opened once.)

 * FIXES #4019.

src/or/config.c

@@ -6251,8 +6251,9 @@ port_cfg_free(port_cfg_t *port)
 /** Warn for every port in <b>ports</b> of type <b>listener_type</b> that is
  * on a publicly routable address. */
 static void
-warn_nonlocal_client_ports(const smartlist_t *ports, const char *portname,
-                           int listener_type)
+warn_nonlocal_client_ports(const smartlist_t *ports,
+                           const char *portname,
+                           const int listener_type)
 {
   SMARTLIST_FOREACH_BEGIN(ports, const port_cfg_t *, port) {
     if (port->type != listener_type)
@@ -6936,7 +6937,8 @@ parse_ports(or_options_t *options, int validate_only,
              options->SocksPort_lines,
              "Socks", CONN_TYPE_AP_LISTENER,
              "127.0.0.1", 9050,
-             CL_PORT_WARN_NONLOCAL|CL_PORT_TAKES_HOSTNAMES|gw_flag) < 0) {
+             ((validate_only ? 0 : CL_PORT_WARN_NONLOCAL)
+              | CL_PORT_TAKES_HOSTNAMES | gw_flag)) < 0) {
     *msg = tor_strdup("Invalid SocksPort configuration");
     goto err;
   }