use backlog -1 on Linux
thanks to Andrei Nigmatulin
diff --git a/src/os/unix/ngx_linux_config.h b/src/os/unix/ngx_linux_config.h
index cf45e54..556651c 100644
--- a/src/os/unix/ngx_linux_config.h
+++ b/src/os/unix/ngx_linux_config.h
@@ -88,7 +88,7 @@
 #endif
 
 
-#define NGX_LISTEN_BACKLOG        511
+#define NGX_LISTEN_BACKLOG        -1
 
 
 #if defined TCP_DEFER_ACCEPT && !defined NGX_HAVE_DEFERRED_ACCEPT