gre: allow live address change

The GRE tap device supports Ethernet over GRE, but doesn't
care about the source address of the tunnel, therefore it
can be changed without bring device down.
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -673,6 +673,7 @@ static bool ipgre_netlink_encap_parms(struct nlattr *data[],
 static int gre_tap_init(struct net_device *dev)
 {
 	__gre_tunnel_init(dev);
+	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 
 	return ip_tunnel_init(dev);
 }