Better reflect the command line version of the socket address arguments,
following the now recommended long-form opt=on syntax.

Complement/fixes commit 9d902d51 "chardev: do not use short form boolean
options in non-QemuOpts character device descriptions".

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>