net: openvswitch: add action error drop reason

Add a drop reason for packets that are dropped because an action
returns a non-zero error code.

Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>