gre6: allow to update all parameters via rtnl

commit 6a61d4db upstream.

Parameters were updated only if the kernel was unable to find the tunnel
with the new parameters, ie only if core pamareters were updated (keys,
addr, link, type).
Now it's possible to update ttl, hoplimit, flowinfo and flags.

Fixes: c12b395a ("gre: Support GRE over IPv6")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/ipv6/ip6_gre.c

@@ -1553,13 +1553,11 @@ static int ip6gre_changelink(struct net_device *dev, struct nlattr *tb[],
 			return -EEXIST;
 	} else {
 		t = nt;
+	}
 
 	ip6gre_tunnel_unlink(ign, t);
 	ip6gre_tnl_change(t, &p, !tb[IFLA_MTU]);
 	ip6gre_tunnel_link(ign, t);
-		netdev_state_change(dev);
-	}
-
 	return 0;
 }