IP TOS module for nginx.

This module was designed to allow setting of ip_tos ip header byte on
outgoing packets sent by nginx.  It may be used to implement smart QoS
and traffic shaping at firewall/router level.

Note that it doesn't try to impose any limits on TOS field and should be used
with care.  At least you probably shouldn't touch two lower bits related
to ECN.

Some TOS related info may be found here:

http://en.wikipedia.org/wiki/Type_of_Service
http://en.wikipedia.org/wiki/Differentiated_services
http://en.wikipedia.org/wiki/Quality_of_Service

Configuration directives:

    ip_tos  (off|0xHH)

        Context: http, server, location
        Default: off

        Switches ip tos setting and specifies value to use.

Usage:

    ip_tos  0x00;

    location /video/ {
        ip_tos  0x10;
    }

Note that setting TOS happens at request start and only if configured, so
keepalive connections may inherit TOS from previous request.  It is good
idea to explicitly set default TOS value at server level (or even at http
level if the same listening socket used by more than one server).

To compile nginx with ip tos module use "--add-module <path>" option to nginx
configure.