Register a yank function to shutdown the socket on yank.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <1f4eeed1d066c6cbb8d05ffa9585f6e87b34aac6.1609167865.git.lukasstraub2@web.de>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>