In EXOS versions prior to 15.3.3 this functionality is not available. In EXOS 15.3.3 a mechanism was introduced to enable Layer 2 protocol tunneling.
debug hal configure vpws forward-L2-bpdu [on | off]
This needs to be set to on (Note: the command will not tab auto complete so it must be fully typed.)
debug hal configure vpws forward-L2-bpdu on
In EXOS 15.6 VPLS support for the Layer 2 Protocol Tunneling (L2PT) feature was added and the above commands were deprecated. Information on using this feature can be found in the following article:How to configure l2pt profile in Extreme Switches