TS 101 671 imports: revert domainID change, strengthn language

Improve the comments describing how HI1NotificationOperations
and HI2Operations modules shall encode identically to
TS 101 671 V3.15.1.

Revert hi1OperationId back to version6(6).
Note: Even though the module was version7(7), this value was version6(6),
as a historical oversight in TS 101 671 V3.13.1 (2015-11).

Revert hi2OperationId back to version18(18).