Don't notify on network switch if source network is validated.

Sometimes we switch away from a network to another (e.g., wifi to
cell data) not because the old network is unvalidated, but
because the score is lowered by a low signal strength.

In this case, don't notify the user of a network switch.

Bug: 31132499
Change-Id: I996a6e00096f8cb864fa9b00b36921725a4edb53
diff --git a/services/core/java/com/android/server/connectivity/LingerMonitor.java b/services/core/java/com/android/server/connectivity/LingerMonitor.java
index 4034877..064a904 100644
--- a/services/core/java/com/android/server/connectivity/LingerMonitor.java
+++ b/services/core/java/com/android/server/connectivity/LingerMonitor.java
@@ -242,6 +242,12 @@
             return;
         }
 
+        // Only show the notification if we switched away because a network became unvalidated, not
+        // because its score changed.
+        // TODO: instead of just skipping notification, keep a note of it, and show it if it becomes
+        // unvalidated.
+        if (fromNai.lastValidated) return;
+
         if (isNotificationEnabled(fromNai, toNai)) {
             notify(fromNai, toNai, forceToast);
         }