Fix venue info notification not displaying

The venue info notification was never displayed, because querying the
notification channel from UserHandle.ALL returns no channel.
Channels must be handled from the NetworkStack (owner) user, not the ALL
user that is used to send notifications.

Bug: 157203874
Test: atest NetworkStackTests; manual: verified showing or disabling the
      notification as owner or alternate user.
Change-Id: I9ce908cebdef81bb524353219f7ee9ead2487056