[Wi-Fi] Fix Wi-Fi picker context menu 'Connect' button

1. Display the Wi-Fi dialog with MODE_CONNECT.
2. Connect with the WifiConfiguration from
   WifiConfigController2#getConfig() if it's available.

Bug: 152826354
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiSettings2
Change-Id: Ifbe2ac30b1c37c8eab3227ac0561fdd2de5cb706