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 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.