MCS - Add macro definitions and rename internal variables.

- Rename 'select_enforced' by 'select_value' and add macro definitions:

MCS_SELECT_NOSELECT
MCS_SELECT_ONDEMANDSELECT
MCS_SELECT_SELECT

- Change 'uint32_t enforced' to 'bool label_strict_enforced'
- Change 'uint32_t private_data' to 'bool privatedata_enabled'

Bug 3438.