When we receive a global and link-local ipv6 next-hop ipv6 address,
normally the link-local one is preferred. This setting allows to use the
global ipv6 instead. This is required if the peer does not answer on
his link-local address.
https://docs.frrouting.org/en/latest/routemap.html#clicmd-setipv6next-hopprefer-global
Pull-Request: https://github.com/vyos/vyatta-cfg-quagga/pull/80