roles/nginx: Turn on tcp_nopush in nginx.conf

It seems tcp_nopush is meant to be used with sendfile in newer
versions of nginx.

See: https://github.com/h5bp/server-configs-nginx/blob/master/nginx.conf
See: https://t37.net/nginx-optimization-understanding-sendfile-tcp_nodelay-and-tcp_nopush.html

Signed-off-by: Alan Orth <alan.orth@gmail.com>

roles/nginx/files/nginx.conf

@@ -29,7 +29,10 @@ http {
     # this option should be disabled as ZFS's ARC caches
     # frequently used files in RAM by default.
     sendfile        on;
-    #tcp_nopush     on;
+
+    # Tell Nginx not to send out partial frames; this increases throughput
+    # since TCP frames are filled up before being sent out. (adds TCP_CORK)
+    tcp_nopush      on;
 
     keepalive_timeout  65s;