Upstream: fixed unexpected tcp_nopush usage on peer connections.

Now tcp_nopush on peer connections is disabled if it is disabled on
the client connection, similar to how we handle c->sendfile.  Previously,
tcp_nopush was always used on upstream connections, regardless of
the "tcp_nopush" directive.

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 47cc6cc..688acd8 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -1556,6 +1556,10 @@
     c->sendfile &= r->connection->sendfile;
     u->output.sendfile = c->sendfile;
 
+    if (r->connection->tcp_nopush == NGX_TCP_NOPUSH_DISABLED) {
+        c->tcp_nopush = NGX_TCP_NOPUSH_DISABLED;
+    }
+
     if (c->pool == NULL) {
 
         /* we need separate pool here to be able to cache SSL connections */