docs: vhost-user: replace _SLAVE_ with _BACKEND_

Backend's message and protocol features names were still
using "_SLAVE_" naming. For consistency with the new naming
convention, replace it with _BACKEND_.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Message-Id: <20230208203259.381326-2-maxime.coquelin@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
1 file changed