Add support for metadata to the Match/Action classes

- Allow to attach some property to Match and Action so they can be
used for passing extra informations, that applications can use.

Change-Id: I4225271d7cd3429b11adb191ae178f541bbd635d
Signed-off-by: Giovanni Meo <gmeo@cisco.com>
Merge "Add support for metadata to the Match/Action classes"