live migration is not using secondary interface

A naive 'virsh migrate --live domU xen+tcp://cross-over-ip' uses the ordinary uplink instead of the requested IP address. According to the documentation an additional option has to be specified to really use the other network interface. However, neither 'tcp://cross-over-ip' nor 'xenmigr:cross-over-ip/' works, the migration does not start. 'xenmigr' was removed with 1dac5fbbbb06a0341e8087dc33af75c8352d77a4 and 7ed598438687feaddaf0a653d7cbb8a1c1ad4933, but the docs were not updated. This leaves 'tcp://ip'. What change needs to be done in the driver to support a secondary interface? Olaf