datapath: ip6_gre: Split up ip6gre_tnl_change()

datapath: ip6_gre: Split up ip6gre_tnl_change()

commit a6465350ef495f5cbd76a3e505d25a01d648477e
Author: Petr Machata <petrm@mellanox.com>
Date:   Thu May 17 16:36:33 2018 +0200

    net: ip6_gre: Split up ip6gre_tnl_change()

    Split a reusable function ip6gre_tnl_copy_tnl_parm() from
    ip6gre_tnl_change(). This will allow ERSPAN-specific code to
    reuse the common parts while customizing the behavior for ERSPAN.

    Fixes: 5a963eb61b7c ("ip6_gre: Add ERSPAN native tunnel support")
    Signed-off-by: Petr Machata <petrm@mellanox.com>
    Acked-by: William Tu <u9012063@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>
Tested-by: Greg Rose <gvrose8192@gmail.com>