[ThroughputScorer] Simplify last-selected bonus

Change the way that a last-selected network bonus is applied.
Instead of adding a very large value that fades to zero over time,
just set the score to a value large enough to guarantee that this
network will get selected during a configurable time interval.

The default interval is 480 minutes (8 hours).

Bug: 151564543
Test: atest com.android.server.wifi
Change-Id: I2431415138adba1f16f86982f56275c4240ad81d
diff --git a/service/res/values/config.xml b/service/res/values/config.xml
index a6d9481..76741b1 100644
--- a/service/res/values/config.xml
+++ b/service/res/values/config.xml
@@ -93,9 +93,8 @@
     <integer translatable="false" name="config_wifiFrameworkCurrentNetworkBonus">20</integer>
     <integer translatable="false" name="config_wifiFrameworkSecureNetworkBonus">10</integer>
 
-    <!-- The bonus for the last-selected network starts out very large to override the category
-         boundaries. -->
-    <integer translatable="false" name="config_wifiFrameworkLastSelectionBonus">1999</integer>
+    <!-- The duration in minutes to strongly favor the last-selected network over other options. -->
+    <integer translatable="false" name="config_wifiFrameworkLastSelectionMinutes">480</integer>
 
     <!-- Integer specifying the min packet Tx/Rx rates in packets per second to be considered
          active traffic so that network selection and scan could be skipped-->