Post notifications per subid

Since SST exists per subscription, we should post notifications per
subId. We do this here by posting/canceling notifications with the
optional "tag" argument, so that the unique combination of
tag+notification-id itentifies each notification.

Bug: 69928579
Test: manually verified that mPrevSubId is correct when
cancelAllNotifications is called on sim removal
Change-Id: Ib8836ee75715e7f274a3c365e88c30d8c7c62514