QUIC: set to standard TLS codepoint after draft versions removal.

This is to ease transition with oldish BoringSSL versions,
the default for SSL_set_quic_use_legacy_codepoint() has been
flipped in BoringSSL a1d3bfb64fd7ef2cb178b5b515522ffd75d7b8c5.

src/event/quic/ngx_event_quic_ssl.c

@@ -567,7 +567,7 @@ ngx_quic_init_connection(ngx_connection_t *c)
 #endif
 
 #if BORINGSSL_API_VERSION >= 13
-    SSL_set_quic_use_legacy_codepoint(ssl_conn, qc->version != 1);
+    SSL_set_quic_use_legacy_codepoint(ssl_conn, 0);
 #endif
 
     qsock = ngx_quic_get_socket(c);