The site-of-origin. This site-of-origin is added to the extended
communities for all routes received from the peer. When sending routes
to this peer-group all routes with this extended community are filtered.
The null extended community (all 8 bytes zero) means that no
site-of-origin is configured for this peer. It is not allowed to set
this object to any extended community other than a site-of-origin type
of extended community or null.