odp-util: Remove unnecessary TOS ECN bits rewrite for tunnels

odp-util: Remove unnecessary TOS ECN bits rewrite for tunnels

For tunnels, TOS ECN bits are never wildcard for the reason that they
are always inherited. OVS will create a rewrite action if we add rule
to modify other IP headers. But it also adds an extra ECN rewrite for
the action because of this ECN un-wildcarding.

It seems no error because the ECN bits to be changed are same in this
case. But as rule can't be offloaded to hardware, the unnecssary ECN
rewrite should be removed.

Signed-off-by: Jianbo Liu <jianbol@mellanox.com>
Reviewed-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>