VPN Hotspot 2.0: Client+ (#39)

Fix #13, #38. I don't have a lot of confidence that this would work very well for every device.

Also here's an SQL command that hopefully somebody could make into the app for me: `SELECT TrafficRecord.mac, SUM(TrafficRecord.sentPackets), SUM(TrafficRecord.sentBytes), SUM(TrafficRecord.receivedPackets), SUM(TrafficRecord.receivedBytes) FROM TrafficRecord LEFT JOIN TrafficRecord AS Next ON TrafficRecord.id = Next.previousId WHERE Next.id IS NULL GROUP BY TrafficRecord.mac;`

mobile/src/main/java/be/mygod/vpnhotspot/LocalOnlyHotspotService.kt

@@ -33,7 +33,7 @@ class LocalOnlyHotspotService : IpNeighbourMonitoringService() {
     private var routingManager: LocalOnlyInterfaceManager? = null
     private var receiverRegistered = false
     private val receiver = broadcastReceiver { _, intent ->
-        val ifaces = TetheringManager.getLocalOnlyTetheredIfaces(intent.extras)
+        val ifaces = TetheringManager.getLocalOnlyTetheredIfaces(intent.extras ?: return@broadcastReceiver)
         debugLog(TAG, "onTetherStateChangedLocked: $ifaces")
         check(ifaces.size <= 1)
         val iface = ifaces.singleOrNull()
@@ -45,7 +45,7 @@ class LocalOnlyHotspotService : IpNeighbourMonitoringService() {
         } else {
             val routingManager = routingManager
             if (routingManager == null) {
-                this.routingManager = LocalOnlyInterfaceManager(iface)
+                this.routingManager = LocalOnlyInterfaceManager(this, iface)
                 IpNeighbourMonitor.registerCallback(this)
             } else check(iface == routingManager.downstream)
         }