ui: fix regression handling bare 'websocket' option to -vnc

The -vnc argument is documented as accepting two syntaxes for
the 'websocket' option, either a bare option name, or a port
number. If using the bare option name, it is supposed to apply
the display number as an offset to base port 5700. e.g.

  -vnc localhost:3,websocket

should listen on port 5703, however, this was broken in 2.3.0 since

  commit 4db1462
  Author: Gerd Hoffmann <kraxel@redhat.com>
  Date:   Tue Sep 16 12:33:03 2014 +0200

    vnc: switch to QemuOpts, allow multiple servers

instead qemu tries to listen on port "on" which gets looked up in
/etc/services and fails.

Fixes bug: #1455912

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170203120649.15637-2-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/vnc.c

@@ -3558,7 +3558,13 @@ void vnc_display_open(const char *id, Error **errp)
                 wsaddr->type = SOCKET_ADDRESS_KIND_INET;
                 inet = wsaddr->u.inet.data = g_new0(InetSocketAddress, 1);
                 inet->host = g_strdup(saddr->u.inet.data->host);
-                inet->port = g_strdup(websocket);
+                if (g_str_equal(websocket, "") ||
+                    g_str_equal(websocket, "on")) {
+                    inet->port = g_strdup_printf(
+                        "%d", (int)baseport + 5700);
+                } else {
+                    inet->port = g_strdup(websocket);
+                }
 
                 if (to) {
                     inet->has_to = true;