nexthop: fix IPv6 route referencing IPv4 nexthop

...

CVE-2021-0286

A vulnerability in the handling of exceptional conditions in Juniper Networks Junos OS Evolved EVO allows an attacker to send specially crafted packets to the device, causing the Advanced Forwarding Toolkit manager evo-aftmand-bt or evo-aftmand-zx process to crash and restart, impacting all traff...