For similar reasons as commit 3af16718 ("spice: flush on GL update
before notifying client"), vhost-user-gpu must ensure the GL state is
flushed before sharing its rendering result.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210312100108.2706195-3-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>