NetworkCallback.onLost should only clear primary wifi network

NetworkCallback.onLost may be called for secondary wifi networks, but
this results in the wifi info being cleared from the status bar. We
should instead only clear the wifi info if the lost network is the
primary network.

Bug: 236368704
Test: make RunSettingsLibRoboTests -j40
Change-Id: Iafd380c6b651921c17e21db11ca94541b0a6e738