Accept PROXY protocol

[Lineconnect]

> https://github.com/FreeRADIUS/freeradius-server/commit/54c5ec1da6396bad2ab48
> 2fbdb33ac6ebf86feaa
> >  It's probably less than 1000 lines of code to add this for TCP/TLS
> >  connections.  But the developers are largely booked with a ton of other
> >  things, so this is on the "nice, but perhaps one day" list.
> $ git diff 2f2db87b0 src/main/tls_listen.c  | wc -l
>      298
Wow. Big thanks for your work!

> For anyone who wants PROXY protocol support, please try v3.0.x.  Please
> also suggest documentation updates, specifically comments on configuring
> haproxy.

We will test in the next days. As we're using Traefik as forwarder, i can only 
post configuration from that site. 

Best regards, 
Lineconnect