net: prestera: acl: add support for 'egress' rules

The following is now supported:

  $ tc qdisc add PORT clsact
  $ tc filter add dev PORT egress ...

Signed-off-by: Maksym Glubokiy <maksym.glubokiy@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>