vhost: fix the fd leak

vhost: fix the fd leak

When the vhost-user reconnect to the backend, the notifer should be
cleanup. Otherwise, the fd resource will be exhausted.

Fixes: f9a09ca3ea ("vhost: add support for configure interrupt")
Signed-off-by: Li Feng <fengli@smartx.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20230731121018.2856310-2-fengli@smartx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
(cherry picked from commit 18f2971ce403008d5e1c2875b483c9d1778143dc)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>