refactor: sync `isOnline` status with firmware (2 hours)

app/src/main/java/com/geeksville/mesh/database/entity/NodeEntity.kt

@@ -159,7 +159,7 @@ data class NodeEntity(
     val isOnline: Boolean
         get() {
             val now = System.currentTimeMillis() / 1000
-            val timeout = 15 * 60
+            val timeout = 2 * 60 * 60
             return (now - lastHeard <= timeout)
         }