1. Add a new directive proxy_kernel_network_stack :
Syntax: proxy_kernel_network_stack on | off;
Default: proxy_kernel_network_stack off;
Context: http, stream, mail, server
This directive is available only when NGX_HAVE_FF_STACK is defined.
Determines whether proxy should go throught kernel network stack or fstack.
2.Update F-Stack_Nginx_APP_Guide.md