Always use SSID average for SpeedLabel.

When showing the SpeedLabel for the connected network, continue to use
the SSID based average rather than switching to the curve for the known
AP. This addresses changes in SpeedLabel from when the user selects a
network vs when it appears in the connected section.

Bug: 63073866
Test: runtest --path
frameworks/base/packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/AccessPointTest.java

Change-Id: I06edc1ca4b1b5c8e8615f48c000544ea22a6bbbd