vnc: fix reverse mode

vnc: fix reverse mode

vnc server in reverse mode (qemu -vnc localhost:$nr,reverse) interprets
$nr as display number (i.e. with 5900 offset) in recent qemu versions.
Historical and documented behavior is interpreting $nr as port number
though. So we should bring code and documentation in line.

Given that default listening port for viewers is 5500 the 5900 offset is
pretty inconvinient, because it is simply impossible to connect to port
5500.  So, lets fix the code not the docs.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1489480018-11443-1-git-send-email-kraxel@redhat.com