Correct backport for ip6_gre: release cached dst on tunnel removal

There was an error in the backport, which is now fixed.
Reported-by: Francesco Ruggeri <fruggeri@aristanetworks.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

net/ipv6/ip6_gre.c

@@ -360,6 +360,7 @@ static void ip6gre_tunnel_uninit(struct net_device *dev)
 	struct ip6_tnl *t = netdev_priv(dev);
 	struct ip6gre_net *ign = net_generic(t->net, ip6gre_net_id);
 
+	ip6gre_tunnel_unlink(ign, t);
 	ip6_tnl_dst_reset(netdev_priv(dev));
 	dev_put(dev);
 }