[neutron][tap-as-a-service] ERSPAN support

Hello,

I'd like to add ERSPAN support to the Tap-as-a-Service project.

I've currently implemented a prototype that can be used with networking-vpp: https://opendev.org/x/networking-vpp The modified version of tap as a service is available here (The API has been extended to support ERSPAN): https://github.com/jbeuque/tap-as-a-service

I don't know who maintains the Taas project. But if you think adding this functionality could be useful, please contact me. (Please take the modified version of Taas as a proposal to be discussed).

Regards, Jean-Bernard Beuque