net: prestera: add support for egress traffic mirroring

This enables adding matchall rules for egress:

  tc filter add .. egress .. matchall skip_sw \
    action mirred egress mirror dev ..

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