bind()s to address LST-ADDR on port LST-PORT and retransmits UDP
packets received to addresses(s) DST-ADDR(s) on port DST-PORT,
with modified headers to reflect the new target.

To receive broadcast traffic, use a LST-ADDR of 0.0.0.0.  If
a program is already listening on LST-PORT on LST-ADDR, you may
listen on a broadcast address such as 255.255.255.255.

Steam broadcasts to a number of different ports, so it is
sufficient to listen on a different port to your game server.
e.g. a LST-PORT of 27016 and a DST-PORT of 27015 will let you
listen on a different port to a game server, but for it to still
directly receive packets that were broadcast.

Revision history:

1st October 2014
- udprelay-1.1
-- Add the ability to send to a broadcast address

29th September 2010
- udprelay-1.0
-- Initial release