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

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index ec553ec..51c8b0a 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -475,6 +475,7 @@
         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;
     }