This reverts commit 5f6a61f.

Signed-off-by: Louis Scalbert <[email protected]>

Do not add an IPv6 link-local nexthop if the originating peer does not
provide one and the nexthop-local unchanged setting is enabled.

Signed-off-by: Louis Scalbert <[email protected]>

If the "nexthop-local unchanged" setting is enabled, it preserves the
IPv6 link-local nexthop from the originating peer. However, if the
originating and destination peers are not on the same network segment,
the originating peer's IPv6 link-local address will be unreachable from
the destination peer.

In such cases, reset the IPv6 link-local nexthop, even if "nexthop-local
unchanged" is set on the destination peer.

Signed-off-by: Louis Scalbert <[email protected]>

Add bgp_nexthop_ipv6 to check the ipv6 link-local nexthop conformity in
several situations.

Signed-off-by: Louis Scalbert <[email protected]>