Don't consider NOARP devices as Ethernet devices.

NStorm reported a failure of ARP ping scan on OpenVZ venet devices,
which don't have a MAC address and can't do ARP. We don't keep interface
flags such as NOARP at the target level, so check whether the interfaces
returned by libdnet are both INTF_TYPE_ETH and don't have
INTF_FLAG_NOARP set; otherwise call them "other" interfaces.

http://seclists.org/nmap-dev/2013/q1/349
http://openvz.org/Virtual_network_device