vRouter can not set the tunnel type to MPLSoverUDP

[Groundsea]

Hi expert,
I have set the tunnel_type field in contrail-vrouter-agent.conf with MPLSoUDP, and I also set the SDNGW with UDP tunnel. The packets that SDN-GW sent to vRouter has already changed to MPLSoUDP, but the packets sent from vRouter to SDN-GW was still MPLSoGRE. So is there anything I got missed?
Any help would be appreciated!
BTW: vRouter is V3.2.x, SDN-GW is MX240.

BR.
Haifeng.