[Settings] Wifi Setup responds to other connection state change

Made use of the two new extras isNetworkRequired and ifWifiRequired in
deciding the ui state of the wifi setting. The CL that adds these
extras in setup wizard is here (http://ag/612291).

Added logic to update the next ("skip") button state accordingly:

(1) "Skip" button should be enabled if
    - wifi is not required and network is not required
    - or wifi is not required, but network is required, and we have a
      valid network connection

(2) "Skip" button should be disabled if
    - wifi is required
    - or wifi is not required, but network is required, and we have
      no valid network connection

Note that the newly added logic is only run if wifi is not connected. If
wifi is already connected, the next button will show "next" and be
enabled.

This fixes the bug where wifi settings in setup wizard does not respond
to mobile data connection change.

Bug: 18783746
Change-Id: I155dcb158f790dd96a71099339f64b64cc647da0