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>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 4f4bf5b..942576e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -673,6 +673,7 @@
 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);
 }