ip_tunnel: Add fallback tunnels to the hash lists

Currently we can not update the tunnel parameters of
the fallback tunnels because we don't find them in the
hash lists. Fix this by adding them on initialization.

Bug was introduced with commit c544193214
("GRE: Refactor GRE tunneling code.")

Cc: Pravin Shelar <pshelar@nicira.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_tunnel.c

@@ -853,8 +853,10 @@ int ip_tunnel_init_net(struct net *net, int ip_tnl_net_id,
 	/* FB netdevice is special: we have one, and only one per netns.
 	 * Allowing to move it to another netns is clearly unsafe.
 	 */
-	if (!IS_ERR(itn->fb_tunnel_dev))
+	if (!IS_ERR(itn->fb_tunnel_dev)) {
 		itn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL;
+		ip_tunnel_add(itn, netdev_priv(itn->fb_tunnel_dev));
+	}
 	rtnl_unlock();
 
 	return PTR_RET(itn->fb_tunnel_dev);