Cannot set autostart for transient network

Error:

root@earth:/etc/libvirt# virsh net-autostart bridge
error: failed to mark network bridge as autostarted
error: Requested operation is not valid: cannot set autostart for transient network

Fix:

root@earth:/etc/libvirt# virsh net-edit bridge

Make some silly change (like add a comment).

root@earth:/etc/libvirt# virsh net-autostart bridge