MAJOR: listen section: don't use first bind port anymore when no server ports are...

MAJOR: listen section: don't use first bind port anymore when no server ports are provided

Up to HAProxy 1.7-dev3, HAProxy used to use the first bind port from it's
local 'listen' section when no port is configured on the server.

IE, in the configuration below, the server port would be 25:

  listen smtp
   bind :25
   server s1 1.0.0.1 check

This way of working is now obsolete and can be removed, furthermore it is not
documented!

This will make the possibility to change the server's port much easier.