[WIFI][SYSUI] Display Wi-Fi icon in status bar if it is the default network

Wi-Fi icon was removed from status bar if it doesn't have internet
access. Rationale was that it gives users incorrect impression that
wi-Fi is enabled whereas in reality cellular is used.

However, in cases where there is no cellular Wi-Fi may be the default
network even if it has no internet access. In such cases, Wi-Fi is the
default network, always show it in the status bar.

Bug: 136473125
Test: atest NetworkControllerWifiTest
Test: visual inspection
Change-Id: I0ec189e2340d3280165cafd8747a7456f7e950f5