Hi
you can try the last driver Mellanox OFED Linux (MLNX_OFED)
in the release notes of MLNX_OFED 3.4-1.0.0.0 Release Notes mentioned that added VST Q-in-Q feature.
VST Q-in-Q Added support for Q-in-Q encapsulation per VF in Linux (VST) for ConnectX-3 Pro adapter cards.
Thanks,
Talat