cannot perform tunnelled migration without using peer2peer flag

[zhang xintao <zhang.kvm@xxxxxxxxx>]

Dear All
         I try to migration a kvm guest os to another host failed
         server: ubuntu 11.04 server
         virsh:migrate --live --tunnelled vm1   qemu+ssh://192.168.10.3/system
         error:Requested operation is not valid:cannot perform
tunnelled migration without using peer2peer flag