Bug 992129 - Generate voicemail notifications that are DSDS compliants

The computed voicemail tag needs to be aware of the SIM card, otherwise
we may overwrite one notification for one SIM with notification for
another one. We rely on the serviceId for this.
Merge pull request #17986 from lissyx/bug992129

Bug 992129 - Generate voicemail notifications that are DSDS compliants r=etienne_s