virtio-serial: propagate guest_connected to the port on post_load

virtio-serial: propagate guest_connected to the port on post_load

When migrating a host with with a spice agent running the mouse becomes
non operational after the migration due to the agent state being
inconsistent between the guest and the client.

After migration the spicevmc backend on the destination has never been notified
of the (non 0) guest_connected state. Virtio-serial holds this state
information and migrates it, this patch properly propagates this information
to virtio-console and through that to interested chardev backends.

rhbz #725965

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Message-id: 1364292483-16564-11-git-send-email-hdegoede@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>