gre: allow changing mac address when device is up

There is no need to require forcing device down on a Ethernet GRE (gretap)
tunnel to change the MAC address.
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -649,6 +649,7 @@ static void ipgre_tap_setup(struct net_device *dev)
 {
 	ether_setup(dev);
 	dev->netdev_ops		= &gre_tap_netdev_ops;
+	dev->priv_flags 	|= IFF_LIVE_ADDR_CHANGE;
 	ip_tunnel_setup(dev, gre_tap_net_id);
 }