Update Solid's support to org.freedesktop.NetworkManager.Device
interface to NM-0.8.2. Two properties have been added: IpInterface and
FirmwareMissing. Now only Ip6Config is still missing from that NM's
interface.

IpInterface is slighty different from the already supported Interface
property. In most cases they return the same value, but for serial
devices (dial-up modems, Gsm, Cdma, Bluetooth) Interface returns the
serial device (/dev/tty*, /dev/ttyACM* /dev/ttyUSB*, /dev/rfcomm*) and
IpInterface returns connection's IP interface (usually ppp0).