ipv4: Handle ipv6 gateway in fib_good_nh

Update fib_good_nh to handle an ipv6 gateway.
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -1909,8 +1909,14 @@ static bool fib_good_nh(const struct fib_nh *nh)
 
 		rcu_read_lock_bh();
 
+		if (likely(nh->fib_nh_gw_family == AF_INET))
 			n = __ipv4_neigh_lookup_noref(nh->fib_nh_dev,
 						   (__force u32)nh->fib_nh_gw4);
+		else if (nh->fib_nh_gw_family == AF_INET6)
+			n = __ipv6_neigh_lookup_noref_stub(nh->fib_nh_dev,
+							   &nh->fib_nh_gw6);
+		else
+			n = NULL;
 		if (n)
 			state = n->nud_state;