[Wi-Fi] Support disconnect button for connected Wi-Fi AP

Connect button becomes Disconnect button if the Wi-Fi AP
is connected.

Bug: 135891885
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=WifiDetailPreferenceController2Test
Change-Id: I0e0d485385294658170da3d37bc1cc1f8748468f
3 files changed