Update the title & description of notification

Refer to the UX design doc to fix the title & description.

Bug: 150903640
Test: 1. Build pass
      2. atest NetworkStackTests
      3. Manual test to see if the title & description are shown
      as expected

Change-Id: I5ab49a3b5b220e144c69627eb9d02c6ddc438716
Merged-In: I354f9f19aa4d8057b49833107c8bd4d9c67d5525
(cherry picked from commit 07c90583)