Hello,

I am proposing a fix for a segfault encountered in bird6, in the nexthop_compare_node function.

This patch adds checks for validating that x->iface and y->iface are not null before accessing their index field.

I initially proposed a fix on calico's bird fork : https://github.com/projectcalico/bird/pull/117 but I was asked to propose it to the official repo.

Please find the full patch attached.
Best regards,