bgpd: Allow sending Origin Validation State extended community over EBGP-OAD

bgpd: Allow sending Origin Validation State extended community over EBGP-OAD

https://datatracker.ietf.org/doc/html/draft-uttaro-idr-bgp-oad#section-3.13

Extended communities which are non-transitive across an AS boundary MAY be
advertised over an EBGP-OAD session if allowed by explicit policy configuration.

If allowed, all the members of the OAD SHOULD be configured to use the same
criteria.

For example, the Origin Validation State Extended Community, defined as
non-transitive in [RFC8097], can be advertised to peers in the same OAD.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>