Support USB tethering

Support USB tethering

To enable USB tethering, you must run the following two commands after configuring the USB endpoint.

1. /sbin/ifconfig usb0 192.168.129.3 up
2. /Sbin/route add -net 192.168.129.0 netmask 255.255.255.0 dev usb0

These commands are not directly executed by deviced, but are delegated to rndis.service.
The reason is to use the already implemented structure (sdbd.service and mtp-response.service).

The patch has been split into deviced and libdeivce-node.
The rndis.service is in deviced, and the code to run rndis.service is in libdevice-node.

Connected patch: "Support USB tethering" commit on deviced.

Change-Id: If4f64310c28cd91f4d2864365127a088e977e26a