28: HTTP/3 UDP path ignores CURL_SOCKOPT_ALREADY_CONNECTED, reconnects callback-provided socket

When `CURLOPT_SOCKOPTFUNCTION` returns `CURL_SOCKOPT_ALREADY_CONNECTED`, the HTTP/3 (QUIC) UDP code path ignores it and calls `connect()` anyway, silently reassociating the application-provided socket to a different peer. The TCP path has the correct check. This violates the documented callback …

// lib/cf-socket.c, inside cf_tcp_connect(), after cf_socket_open():
if(cf->connected) {
  *done = TRUE;
  return CURLE_OK;
}