[TNU02] Update tethering notification by active data subid

Tethering notification can be customized by different subid. Thus
update notification when active data subid changed.

Bug: 122085773
Bug: 130596698
Test: atest TetheringTests
Change-Id: I799d713326cfbf4dc96c712c6b15ed5a4ac18dd2
Merged-In: I799d713326cfbf4dc96c712c6b15ed5a4ac18dd2
(cherry picked from aosp/1209984)