HTTP/2: fixed c->timedout flag on timed out connections.

Without the flag, SSL shutdown is attempted on such connections,
resulting in useless work and/or bogus "SSL_shutdown() failed
(SSL: ... bad write retry)" critical log messages if there are
blocked writes.

src/http/v2/ngx_http_v2.c

@@ -475,6 +475,7 @@ ngx_http_v2_write_handler(ngx_event_t *wev)
         ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
                        "http2 write event timed out");
         c->error = 1;
+        c->timedout = 1;
         ngx_http_v2_finalize_connection(h2c, 0);
         return;
     }