Call handleNetworkDisconnect before trasition to disconnected state

ClientModeImpl starts ignoring disconnect messages once it's
transitioned to disconnected state. Therefore need to make sure that we
always call handleNetworkDisconnect before the transition to clean up
internal states and to sendout the disconnect broadcast.

Bug: 195755234
Bug: 195574603
Test: atest com.android.server.wifi
Test: Manually verified that the device no longer gets stuck on
"authenticating..." when connecting with the wrong password.

Change-Id: I3452b93bd65259a6e9d98942344d904afe89d4b6