hw/virtio: Support set_config() callback in vhost-user-base

hw/virtio: Support set_config() callback in vhost-user-base

The Virtio input device invokes set_config() callback for retrieving
the event configuration info, but the callback is not supported in
vhost-user-base.

This patch adds support set_config() callback in vhost-user-base.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20231120043721.50555-2-leo.yan@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240104210945.1223134-9-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>