Move PBB actions to their proper place in enum

Because PBB actions were in wrong place in enum , they were assigned
numbers 21 and 22 where they should have 26 and 27 according to the
OFP 1.3.1 spec.

Refs: FlowForwarding/LINC-Switch#68
Add explicit enum numbering to action types list

Because action types numbering has gaps according to OFP specification,
explicit enumeration for each action type was added, to avoid confusion
regarding numbers for different action types, and to avoid errors in the
future, when adding new action types.

Refs: FlowForwarding/LINC-Switch#68