Update WifiStateChangedListener CTS for immediate callback

WifiStateChangedListener was updated to give an immediate callback upon
registration. Update the CTS test to account for this.

Flag: com.android.wifi.flags.wifi_state_changed_listener

Bug: 3500570
Test: atest WifiManagerTest
Change-Id: I58450884cf60431e317c2e46e8203cbd51482051