Qdisc graft operation of offload-capable qdiscs performs a few
extra steps which are identical among all the qdiscs.  Add
a helper to share this code.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NJohn Hurley <john.hurley@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>