NetworkManager: isWifiOn isConnected consistent usage.

cervantes kindle kobo remarkable: use sysfs carrier file to determine connection state

cleanup hasWifiManager checks

gateway check: use ip if available

Fixes: #10087
Closes: #10092

frontend/device/android/device.lua

@@ -292,12 +292,13 @@ function Device:initNetworkManager(NetworkMgr)
         android.openWifiSettings()
     end
 
-    function NetworkMgr:isWifiOn()
+    function NetworkMgr:isConnected()
         local ok = android.getNetworkInfo()
         ok = tonumber(ok)
         if not ok then return false end
         return ok == 1
     end
+    NetworkMgr.isWifiOn = NetworkMgr.isConnected
 end
 
 function Device:performHapticFeedback(type)